Question 1

According to drinking-water guidelines and common standards, the acceptable pH range for public water supplies should be maintained approximately within:

Accepted Answer

Introduction / Context: pH control is crucial for corrosion management, coagulation efficiency, taste, and disinfection stability. Most standards specify a desirable pH band to balance consumer acceptability and infrastructure protection. Given Data / Assumptions: Treated potable water distribution conditions. Commonly cited desirable range in many national standards. Aim to minimize corrosion/scale while maintaining treatment efficacy. Concept / Approach: pH below about 6.5 can be corrosive to metals, while pH above ~8.5 can cause scaling and interference with certain treatment processes or taste. The 6.5–8.5 range is widely accepted as the desirable band for distribution systems, with utilities often targeting narrower control bands depending on alkalinity and corrosion indices. Step-by-Step Solution: Identify range that balances corrosion vs scaling.Select the standard desirable band ≈ 6.5–8.5.Confirm consistency with typical drinking-water guidelines. Verification / Alternative check: Cross-refer to national standards and WHO guidance indicating the same typical desirable range. Why Other Options Are Wrong: Lower ranges (4.5–6.5) are too acidic; 8.5–10.5 is excessively alkaline for most systems and can cause taste/scaling issues. Common Pitfalls: Assuming the range is a rigid legal limit everywhere; exact compliance bands may vary by jurisdiction, but 6.5–8.5 remains a common exam value. Final Answer: 6.5 to 8.5

Question 2

In conventional surface-water treatment plants, which chlorination practice is regarded as the standard step applied after filtration to ensure a disinfectant residual in the distribution system?

Accepted Answer

Introduction / Context: Chlorination strategies can be placed at different points in the treatment train to achieve specific goals (algae control, taste/odor management, primary disinfection, residual maintenance). The standard practice that ensures pathogen inactivation of filtered water and maintains a residual in the network is post-chlorination. Given Data / Assumptions: Conventional treatment: coagulation, flocculation, sedimentation, filtration. Need for a stable disinfectant residual entering the distribution system. Compliance with microbial safety objectives. Concept / Approach: Post-chlorination after filtration treats clarified, low-turbidity water, maximizing disinfectant efficacy and permitting a controlled residual to persist in the distribution system for protection against recontamination. Other placements (pre-chlorination) serve different objectives and may form undesirable by-products if not managed carefully. Step-by-Step Solution: Place chlorination point after filtration to minimize chlorine demand from particulates/organics.Set dose to meet CT requirements and leave an appropriate residual.Confirm regulatory targets for residual at system entry. Verification / Alternative check: Standard operating procedures and texts identify post-chlorination as the default/standard disinfecting step; alternative strategies are supplemental or situational. Why Other Options Are Wrong: Plain or pre-chlorination alone may not assure residual after filtration and can increase by-product formation. Double chlorination is not universally required and is not termed the standard practice. Common Pitfalls: Confusing pre-chlorination (process aid) with the final disinfection and residual maintenance step; overlooking contact time and residual monitoring needs. Final Answer: post-chlorination (after filtration, before distribution)

Question 3

Water quality concept: At what pH value would the alkalinity of water be at its maximum (considering the standard pH scale used in water treatment)?

Accepted Answer

Introduction / Context: Alkalinity in water treatment refers to the acid-neutralizing capacity of water, primarily due to hydroxide, carbonate, and bicarbonate species. The pH scale governs the distribution of these species. Understanding where alkalinity peaks helps operators manage coagulation, corrosion control, and stabilization. Given Data / Assumptions: Standard pH scale from 0 to 14 in aqueous systems. Alkalinity is the capacity to neutralize strong acid to a specific endpoint (often pH about 4.5). Speciation of carbonate system depends on pH. Concept / Approach: Alkalinity increases as pH rises because more bases (HCO3−, CO3^2−, and OH−) are present. At very high pH, hydroxide and carbonate dominate, maximizing neutralizing capacity for an equivalent total inorganic carbon. Therefore, the upper end of the pH scale corresponds to maximum alkalinity potential. Step-by-Step Solution: Recognize alkalinity species: OH−, CO3^2−, HCO3−.As pH increases, equilibria shift toward CO3^2− and OH−, increasing alkalinity.Within the standard 0–14 pH range, the highest alkalinity occurs at the highest pH value.Therefore, select pH = 14 as the point of maximum alkalinity on this scale. Verification / Alternative check: Titration curves show greater acid required to reach the endpoint from high-pH waters than from neutral or low-pH waters, confirming increased alkalinity with rising pH. Why Other Options Are Wrong: Zero / less than 7: Acidic to neutral conditions have low alkalinity. More than 7: True that alkalinity increases above 7, but the maximum within the scale is specifically at 14. 21: Not a standard pH value in aqueous systems. Common Pitfalls: Confusing alkalinity with hardness; they are related but distinct. Assuming “more than 7” is the maximum, rather than identifying the upper bound 14. Final Answer: 14.

Question 4

Groundwater abstraction: A strainer-type tube well is generally unsuitable for which kind of aquifer material?

Accepted Answer

Introduction / Context: Strainer-type tube wells use a slotted screen to admit water and exclude formation particles. Suitability depends on aquifer grain size and gradation, which affect screen entrance velocity, headloss, and sand control without excessive development efforts. Given Data / Assumptions: Conventional slotted or wire-wrapped screens. Unconsolidated aquifers with varying sand/gravel sizes. No artificial gravel pack unless explicitly designed for. Concept / Approach: In very coarse gravels, slot sizes required to retain formation are large and hydraulic entrance velocities become unfavorable; moreover, maintaining adequate screen support and preventing structural damage is difficult. Strainer wells are best in fine to medium sands (often with a gravel pack) where slots can exclude fines at acceptable headloss and velocities. Step-by-Step Solution: Classify formation: coarse gravels vs sands.Assess slot selection: coarse gravels need very large slots, undermining sand control and screen strength.Conclude strainer-type is unsuitable for coarse gravels; alternative large-diameter or gravel-packed designs are preferred. Verification / Alternative check: Well design manuals recommend properly graded gravel packs and specific screen types for coarse formations; straight strainer wells without tailored packs are not advised for coarse gravels. Why Other Options Are Wrong: Fine sandy strata / well-graded medium sand: Common and suitable with proper slot size and development. Clean gravels: Similar issues as coarse gravels; however, “coarse gravels” is the clearest unsuitable option. None of these: Not correct since a clearly unsuitable case exists. Common Pitfalls: Selecting slot size by nominal sieve size without considering uniformity coefficient and entrance velocity. Omitting gravel pack where needed, causing sand pumping. Final Answer: coarse gravels.

Question 5

Urban water distribution networks: Which set correctly lists the four major system layouts commonly adopted?

Accepted Answer

Introduction / Context: Water distribution systems are laid out to balance reliability, pressure management, and cost. Recognizing the standard configurations is essential for planning, hydraulic modeling, and fire-flow provision. Given Data / Assumptions: Conventional municipal networks (not including advanced district metered area strategies). Four canonical layouts considered. Concept / Approach: Standard references describe four principal patterns: tree (branched), grid iron (rectangular loops), ring (peripheral loop or circular), and radial (mains feeding from a central source to zones). Each has distinct headloss, redundancy, and serviceability characteristics, often used in combination across a city. Step-by-Step Solution: Identify canonical patterns: tree, grid iron, ring, radial.Check options for exact naming and avoid duplicates (dead end ≈ tree; reticulation is a general term, not a separate canonical pattern).Select the option that lists the conventional four correctly. Verification / Alternative check: Design texts and codes illustrate example layouts and typical use cases, confirming these four as standard archetypes. Why Other Options Are Wrong: Options with “reticulation” or overlapping synonyms misclassify patterns. “Circular” alone is ambiguous—“ring” (loop) is the intended canonical term. Invented sets like “zig-zag” are not recognized patterns. Common Pitfalls: Confusing “dead end” with a distinct fifth pattern; it is simply the tree layout. Assuming one pattern suits an entire city; mixed layouts are common. Final Answer: tree, grid iron, ring and radial.

Question 6

Transient hydraulics in pipelines: The “critical time” for development of water hammer corresponds to which travel time of the pressure wave?

Accepted Answer

Introduction / Context: Water hammer (surge) arises when flow is suddenly altered, sending a pressure wave that travels at acoustic velocity in the liquid–pipe system. The concept of “critical time” is crucial for evaluating whether a given valve-closure schedule will cause maximum surge. Given Data / Assumptions: Single pipeline between valve and reservoir/tank. Wave speed a; pipeline length L. Elastic water and pipe wall properties define a. Concept / Approach: The reflection of the wave at a reservoir boundary and its return to the valve controls transient magnitude. The critical time equals the round-trip travel time 2L/a. Closure faster than this is “sudden,” producing near-Joukowsky surge; slower closure spreads acceleration and reduces peak pressure. Step-by-Step Solution: Compute travel time one-way: t1 = L / a.Round-trip (critical) time: tc = 2L / a.Compare valve-closure time tv: if tv ≤ tc, expect near-maximum surge. Verification / Alternative check: Transient analysis software and classical water-hammer charts confirm that the most severe pressure rise occurs when closure completes within the round-trip time. Why Other Options Are Wrong: “Closing the valve” is an action, not the definition of critical time. One-way travel underestimates the condition that sets peak surge. “Entire network once” is irrelevant in a single-pipe context. Common Pitfalls: Ignoring elastic wave speed reduction due to pipe wall flexibility. Overlooking boundary conditions (air vessel, surge tank) that change reflections. Final Answer: the wave to travel from the valve to the reservoir and back.

Question 7

Aesthetics in potable water: What is the maximum permissible Threshold Odour Number (TON) typically specified for public water supplies?

Accepted Answer

Introduction / Context: Beyond safety, drinking water must be aesthetically acceptable. Threshold Odour Number (TON) quantifies odour detectability by dilution and is used to indicate consumer acceptance and the absence of nuisance compounds from algae, industrial discharges, or disinfection by-products. Given Data / Assumptions: Standard TON test method (serial dilution until odour is just perceptible). Public supply guidelines for finished water. Concept / Approach: Most guidelines accept a TON not exceeding about 3 for potable supplies. Higher odour numbers can prompt complaints and signal treatment deficiencies (e.g., ineffective activated carbon, manganese issues, or reservoir stratification impacts). Step-by-Step Solution: Conduct odour panel test with serial dilutions.Record the maximum dilution at which odour is detectable; that dilution factor equals TON.Verify TON ≤ 3 before distribution to minimize consumer complaints. Verification / Alternative check: Utilities track taste-and-odour events; maintaining TON around or below 3 aligns with good consumer acceptability and many national standards/handbooks. Why Other Options Are Wrong: TON 1–2: While better aesthetically, these are not common upper limits. TON 4–5: Usually considered objectionable; may breach guideline targets. Common Pitfalls: Treating odour control only at the plant and ignoring distribution issues (biofilm, dead-ends). Confusing TON with threshold flavour number; both are related but distinct measures. Final Answer: 3.

Question 8

Dechlorination in water treatment: Which chemical is most commonly applied for removing excess chlorine after disinfection?

Accepted Answer

Introduction / Context: Dechlorination removes free chlorine residual when it could be problematic (e.g., before discharge to receiving waters or prior to processes sensitive to chlorine). Several reducing agents can neutralize chlorine; selection depends on scale, handling, and residual impacts. Given Data / Assumptions: Conventional municipal facility practices. Liquid or gas chemical feed systems available. Concept / Approach: Sulphur dioxide (SO2) is widely used at plant scale due to controllable feed, rapid reaction, and cost. Alternatives include sodium sulphite and sodium thiosulphate, commonly used in laboratory or small-scale applications. Sodium bisulphate is an acidulant, not a standard dechlorinating agent, thus “all the above” is not correct in this list. Step-by-Step Solution: Identify reducing agent suitable for continuous plant operation: SO2.Apply stoichiometric dosage with safety factor; reaction forms sulphate/chloride.Verify zero residual chlorine downstream by DPD test. Verification / Alternative check: Standard operating procedures and design manuals cite SO2 as the predominant dechlorination agent at wastewater and water plants; sodium sulphite/thiosulphate are often used for sampling/dechlorinating small volumes. Why Other Options Are Wrong: Sodium thiosulphate / sodium sulphite: Effective but typically used for small-scale or sampling; not the most commonly applied at plant-scale. Sodium bisulphate: Primarily lowers pH; not a dechlorination standard. All the above: Incorrect because one listed chemical is not appropriate for dechlorination. Common Pitfalls: Over-dosing SO2 causing sulphite carryover and oxygen depletion in receiving waters. Failing to interlock dosing with chlorine feed to avoid simultaneous overdosing. Final Answer: sulphur-dioxide.

Question 9

Groundwater basics: Identify the incorrect statement about the water table and free-surface groundwater conditions.

Accepted Answer

Introduction / Context: Understanding the behavior of the water table is essential for well design, yield prediction, and sustainable groundwater management. Several statements about groundwater dynamics are presented; the task is to identify the incorrect one based on hydrogeologic principles. Given Data / Assumptions: Unconfined aquifer with a true free surface (water table). Seasonal recharge and pumping may influence levels. Heterogeneity and boundary conditions affect responses. Concept / Approach: The water table is an equipotential surface at approximately atmospheric pressure. It fluctuates due to recharge (rainfall, infiltration) and discharge (pumping, baseflow). While pumping rate affects drawdown near wells, a simple direct proportionality between water-table depth and withdrawal rate is not universally valid; it depends on transmissivity, storativity, and boundary effects. The claim that the water table remains stationary is clearly incorrect because natural systems are dynamic. Step-by-Step Solution: Evaluate (a): Free surface equals atmospheric pressure — correct.Evaluate (b): Seasonal rise/fall occurs with recharge/evapotranspiration — correct.Evaluate (c): “Directly proportional” is an oversimplification; response depends on aquifer parameters — not reliably correct but not as blatantly false as (d).Evaluate (d): “Remains stationary” — unequivocally false in natural settings. Verification / Alternative check: Observed hydrographs show clear seasonal and event-driven water-level fluctuations, disproving the notion of a stationary water table. Why Other Options Are Wrong: (a) and (b) are standard hydrogeologic facts. (c) can be conditionally false; however, the clearly incorrect statement is (d), which contradicts observed behavior. (e) “None of these” is not correct because (d) is incorrect. Common Pitfalls: Treating complex aquifer responses as linear proportionalities without considering transmissivity and storativity. Ignoring boundary conditions that control regional water-table gradients. Final Answer: Level of the water table remains stationary.

Question 10

Terminology in hydrology: The process by which water evaporates, condenses to droplets, precipitates, runs off or infiltrates, and ultimately returns to its sources is commonly called what?

Accepted Answer

Introduction / Context: Hydrology describes the continuous movement of water through the atmosphere, lithosphere, and hydrosphere. Different terms are used in textbooks and practice for this integrated process that connects evaporation, condensation, precipitation, runoff, infiltration, and return flows. Given Data / Assumptions: Standard Earth water movement pathways. Synonymous terminology is acceptable if scientifically consistent. Concept / Approach: “Hydrological cycle” and “water cycle” are interchangeable in most contexts. “Evaporation and precipitation cycle” highlights two key phases but implicitly includes intervening storage and flow pathways. Hence, all listed terms (except for contrived or overly narrow phrases) describe the same holistic process. Step-by-Step Solution: Identify if terms refer to the same closed-loop concept of water movement.Confirm that hydrological cycle = water cycle.Recognize that evaporation–precipitation is part of the same cycle. Verification / Alternative check: Educational standards and literature routinely equate “hydrological cycle” with “water cycle,” encompassing evaporation, condensation, precipitation, infiltration, percolation, and runoff. Why Other Options Are Wrong: Individually, (a), (b), and (c) each refer to the same process; selecting only one would be incomplete, hence (d) “all the above” is the most inclusive and correct. Common Pitfalls: Overlooking subsurface processes (percolation to groundwater) when defining the cycle. Forgetting evapotranspiration from vegetation as a major return pathway. Final Answer: all the above..

Question 11

Why are cast iron (C.I.) pipes commonly preferred in water-supply distribution systems? Select the most appropriate reason from the choices given.

Accepted Answer

Introduction / Context: Choosing a pipe material for municipal distribution involves balancing cost, ease of installation, and long-term performance. Cast iron (historically) and ductile iron (modern successor) have been widely used for pressurized buried mains due to their structural robustness and reliable joints. Given Data / Assumptions: Buried, pressurized water-distribution environment. Standard jointing methods (e.g., spigot-and-socket with gaskets/mechanical joints). Corrosion protection (e.g., lining, coatings) is provided as per practice. Concept / Approach: The selection criteria include capital cost, joint reliability, internal pressure capacity, external load resistance (traffic/surcharge), and expected service life. Cast iron has historically met these requirements, which explains its prevalence in legacy networks and its continued relevance via ductile iron. Step-by-Step Solution: Compare materials on cost: C.I. mains are traditionally moderate in capital cost for pressure duty.Assess constructability: standardized joints make installation straightforward.Evaluate durability: wall thickness and stiffness resist internal pressure and external loads.Consider life cycle: with lining/coatings and soil-side protection, long life is achievable. Verification / Alternative check: Many cities with century-old C.I. networks still have segments in service, underscoring longevity when protected from corrosion and surge. Why Other Options Are Wrong: Options (a)–(d) each highlight a true advantage; focusing on only one misses the full picture. Therefore the comprehensive choice is (e) All of the above. Common Pitfalls: Ignoring the need for corrosion control; any ferrous pipe without proper protection may suffer premature deterioration. Final Answer: All of the above

Question 12

Water hardness and its practical ranges for domestic and laundry use Identify the correct set of statements about hardness classification and recommended ranges for different purposes.

Accepted Answer

Introduction / Context: Hardness in water is caused primarily by calcium and magnesium salts. Classifying hardness ranges helps utilities and consumers understand scaling, soap consumption, and taste implications for household and public water-supply applications. Given Data / Assumptions: Hardness expressed as ppm (mg/L) as CaCO3. Typical convention: soft, moderately hard, hard ranges used in water treatment practice. Concept / Approach: Practical guidelines often consider water up to about 75 ppm as soft; above roughly 200 ppm is hard and more likely to cause scaling. For laundry, low hardness minimizes soap consumption and prevents fabric dulling. For drinking, very low hardness can taste flat; a moderate range (about 75–120 ppm) is often acceptable for taste and mineral balance. Step-by-Step Solution: Relate softness: hardness ≤ 75 ppm aligns with “soft”.Classify hard water: > 200 ppm commonly regarded as “hard”.Match use-case: laundry prefers low hardness to reduce soap demand.Taste window: moderate hardness (around 75–120 ppm) is usually palatable. Verification / Alternative check: Consumer guidance and water-utility references similarly bracket these values for residential expectations and appliance care. Why Other Options Are Wrong: Each of (a)–(d) is individually correct; omitting any would give an incomplete picture. Thus (e) “All of the above” is the most complete statement set. Common Pitfalls: Confusing ppm as CaCO3 with mg/L of specific ions; always convert to CaCO3 equivalent for comparison. Final Answer: All of the above

Question 13

Grade aqueducts (drainage carried over a canal): which barrel section is most commonly adopted in practice?

Accepted Answer

Introduction / Context: In cross-drainage works, a grade aqueduct conveys a drainage channel over a canal. The structural and hydraulic design of the drainage barrels must pass design discharges efficiently and economically while fitting within construction constraints. Given Data / Assumptions: Masonry or reinforced concrete construction is used for drainage barrels. Headroom, ease of formwork, and flow capacity are key considerations. Concept / Approach: Rectangular barrels are widely used because they are straightforward to design and build with standard formwork, they stack well for multi-cell arrangements, and they offer predictable hydraulic performance (with smooth transitions and wing walls). Specialized shapes like horse-shoe are common in tunnels, while parabolic or triangular are rare for closed conduits. Step-by-Step Solution: Assess constructability: rectangular forms are simple and economical.Evaluate hydraulics: multi-cell rectangles provide flexibility in width and headroom.Compare alternatives: circular/horse-shoe shapes are less convenient for multi-cell overpasses. Verification / Alternative check: Typical irrigation engineering texts illustrate grade aqueducts with rectangular RCC multi-cell barrels. Why Other Options Are Wrong: Circular (a) is common for pressure flow or culverts, not the most common for grade aqueduct multi-cells. Parabolic (c) and triangular (e) are seldom used as closed conduit sections here. Horse-shoe (d) is more typical for tunnels. Common Pitfalls: Confusing culverts under roadways (often circular) with large multi-cell over-canal aqueducts where rectangular proves practical. Final Answer: Rectangular section

Question 14

Specific capacity (specific yield) of wells: select the correct unit definition Specific capacity is defined as the discharge of a well per unit drawdown. Which unit correctly represents this quantity?

Accepted Answer

Introduction / Context: In groundwater engineering, specific capacity (also called specific yield of a well in pumping-test context) helps compare the performance of wells tapping different aquifers or constructed with different designs. Given Data / Assumptions: Specific capacity = well discharge divided by drawdown at the well during pumping. Drawdown is measured in metres. Discharge is commonly recorded in m^3/hour (or m^3/day). Concept / Approach: Because specific capacity normalizes discharge by drawdown, its dimensional form is volume per time per length. A convenient unit is m^3/hour per metre of drawdown (equivalently m^2/hour). Using only m^3/hour would ignore drawdown; per m^2 is unrelated to the definition. Step-by-Step Solution: Write definition: SC = Q / s, where Q is discharge and s is drawdown.Assign units: Q in m^3/h, s in m → SC in m^3/h/m.Select the option that matches m^3/hour per metre of drawdown. Verification / Alternative check: Dimensional analysis: m^3/h divided by m equals m^2/h, confirming consistency. Why Other Options Are Wrong: (a) and (b) omit drawdown, so they are not “specific”. (d) and (e) introduce area terms not in the definition. Common Pitfalls: Confusing aquifer “specific yield” (a storage parameter) with well “specific capacity”; here we refer to well performance in pumping tests. Final Answer: m^3/hour per metre of drawdown

Question 15

Pipe material most commonly adopted for water-distribution mains in traditional municipal systems:

Accepted Answer

Introduction / Context: Municipal water-distribution mains historically used cast iron due to its pressure capacity, stiffness, and established jointing methods. While modern systems often use ductile iron or plastics, older specifications and many current networks still cite cast/ductile iron as standard. Given Data / Assumptions: Pressurized buried distribution mains carrying potable water. Conventional civil engineering practice context. Concept / Approach: C.I. offered a balance of strength, durability, and ease of joining with spigot-and-socket or mechanical joints. R.C.C. is more common for large sewers or gravity mains; G.I. is used in smaller service connections; Hume pipes refer to concrete pipes more suited for non-pressurized or low-pressure applications. Step-by-Step Solution: Identify legacy and standard practice for pressure mains: cast iron.Eliminate materials primarily used for gravity flow (R.C.C., Hume).Note G.I. usefulness for small diameter services, not trunk distribution mains. Verification / Alternative check: Many city asset registries list extensive C.I./ductile iron networks, evidencing long-term adoption. Why Other Options Are Wrong: R.C.C./Hume pipes are better for gravity sewers and culverts. G.I. is typically for small diameters and limited lengths due to corrosion concerns. Asbestos cement (e) is obsolete for health and durability reasons in many regions. Common Pitfalls: Assuming gravity pipe materials are interchangeable with pressure mains; pressure class and joints matter greatly. Final Answer: Cast iron (C.I.) pipes

Question 16

Primary source for large public water-supply schemes: choose the most important one among the following.

Accepted Answer

Introduction / Context: Public water-supply projects require dependable yield at scale, feasible intake works, and treatability. Among natural sources, rivers typically provide the required volume and replenishment for cities. Given Data / Assumptions: Inland setting with traditional freshwater sources. Large population requiring significant, renewable supply. Concept / Approach: Rivers, fed by watershed runoff and baseflow, offer continuous flow and the potential for impoundment (reservoirs) to smooth seasonal variability. Lakes and ponds may be insufficient in capacity or not proximate; small streams are limited in dependable yield; seawater requires energy-intensive desalination (not typically the first choice unless geography dictates). Step-by-Step Solution: Assess dependable yield: rivers usually rank highest among freshwater inland sources.Consider treatment complexity: surface water treatment trains are well-established.Evaluate scalability: rivers and reservoirs can be engineered to support large abstractions. Verification / Alternative check: Most metropolitan systems worldwide draw from rivers/reservoirs as primary sources. Why Other Options Are Wrong: Lakes/ponds may lack sufficient dependable yield. Streams are typically too small for major cities. Sea water requires desalination—costly and energy-intensive. Common Pitfalls: Ignoring the importance of dependable yield (not just volume at a single time) when selecting a source. Final Answer: Rivers

Question 17

Working pressure rating for cast iron (C.I.) water mains Identify the typical maximum working pressure (approximate) to which C.I. pipes may be subjected in traditional practice.

Accepted Answer

Introduction / Context: Pipe classes are chosen to withstand internal pressure plus surge allowances. Traditional cast iron mains have long been rated by nominal internal pressure capability tied to wall thickness/class. Given Data / Assumptions: Typical historical classes for C.I. water mains in municipal distribution. Working (steady) pressure, not transient surge. Concept / Approach: Widely cited values for C.I. mains place the upper range of routine working pressures around 7 kg/cm^2 (approximately 0.7 MPa), with selection depending on diameter, class, and safety margins for transients. Step-by-Step Solution: Relate pressure class to practical municipal ranges (3–7 kg/cm^2 are common).Identify the upper typical working pressure for many C.I. networks: about 7 kg/cm^2. Verification / Alternative check: Historical specifications and catalogs list similar limits for standard C.I. classes; ductile iron extends capability beyond these values as needed. Why Other Options Are Wrong: 3 or 5 kg/cm^2 may be too conservative for many trunk mains. 10 or 12 kg/cm^2 exceed typical C.I. classes used widely without special design. Common Pitfalls: Not accounting for surge; even at 7 kg/cm^2 steady pressure, surge control (air valves, surge tanks) is vital. Final Answer: 7 kg/cm^2

Question 18

Economic diameter concept for pumping mains If the selected pipe diameter is smaller than the economic (optimum) diameter for a pumping main, which of the following statements is true?

Accepted Answer

Introduction / Context: The economic (optimum) diameter minimizes the total annual cost, which is the sum of capital cost (pipe) and operating cost (pumping energy). Deviating below this diameter reduces capital cost but increases friction losses and energy costs. Given Data / Assumptions: Steady discharge in a pumped main. Economic analysis includes energy cost over the service life. Concept / Approach: Head loss in pipes varies approximately with 1/D^5 (Darcy–Weisbach with velocity terms), so smaller D sharply increases head loss and power consumption. The optimum occurs when the marginal increase in capital cost equals the marginal saving in energy. Step-by-Step Solution: Smaller D → higher velocity → higher friction head (for the same Q).Higher friction head → higher pump head → higher energy cost.Capital cost saving on smaller D is offset and surpassed by energy penalties below the economic diameter. Verification / Alternative check: Classical formulas (e.g., power-cost-based diameter selection) show total annual cost curve convex with a minimum at the economic diameter. Why Other Options Are Wrong: (a), (b), and (c) are each individually correct effects. Hence (d) “All of the above” is the right holistic statement; (e) is false. Common Pitfalls: Selecting diameter solely on material cost without lifecycle energy analysis leads to higher total cost of ownership. Final Answer: All of the above

Question 19

Water supply method based on elevation difference:\r When the reduced level (RL) of the water source is higher than the RL of the consumer's location, how is water generally supplied to the distribution system?

Accepted Answer

Introduction / Context: In water supply engineering, choosing the conveyance method depends heavily on topography. If the water source sits at a higher elevation than the service area, gravity can be used to deliver flow without mechanical pumping. This question checks understanding of when gravity systems are appropriate and why they are preferred when feasible. Given Data / Assumptions: The reduced level (RL) of the source is higher than the RL of the consumer's location. Continuous supply is desired with reliability and energy efficiency. Head losses from friction and minor losses are manageable within the available static head. Concept / Approach: A gravity system relies on potential energy due to elevation difference. Available head (H_avail) equals elevation head minus head losses in pipes and appurtenances. If H_avail remains positive at required flows and pressures, no pumps are needed. Gravity systems minimize operating costs and maintenance tied to electromechanical equipment. Step-by-Step Solution: Identify that source RL > demand RL provides potential energy for flow.Estimate head losses: H_losses = friction loss + minor losses; ensure H_source - H_losses - H_min_pressure > 0.Conclude supply by gravity is feasible and preferred.Recognize pumping is unnecessary when elevation head suffices to meet service pressures. Verification / Alternative check: Hydraulic grade line (HGL) plotting from source to consumer shows a downward slope that stays above required service pressure line. If the HGL remains above minimum pressure nodes, gravity-only is confirmed. Why Other Options Are Wrong: By a pumping system: pumps are needless if gravity head is adequate. Combination of pumping and gravity: used when some zones are higher or distant; not required under the stated condition. “All of these” and “None of these” do not reflect the specific topographic advantage given. Common Pitfalls: Ignoring friction losses that might reduce available head in long mains. Forgetting that local high points can create air pockets or pressure deficits even in overall downhill alignments. Final Answer: By a gravitational (gravity) system

Question 20

Empirical formulas for estimating fire demand in water supply design:\r Which named empirical relationship is commonly cited for calculating a city’s required fire demand?

Accepted Answer

Introduction / Context: Water supply systems must provide adequate fire flow in addition to domestic and industrial demands. Designers often reference empirical formulas derived from historical fire fighting needs and urban densities to estimate the required fire demand quickly. This question checks familiarity with the commonly cited named formulas. Given Data / Assumptions: Urban area requires a planning value for peak fire flow. Empirical formula usage is acceptable at predesign or where detailed risk studies are unavailable. The choices list well-known named relationships. Concept / Approach: Several formulas exist: Kuichling, Freeman, and the National Board of Fire Underwriters (often shortened to “Underwriters”) are among the most frequently mentioned in traditional syllabi. While local codes ultimately govern, the Underwriters formula is widely recognized and historically used to set conservative fire demand values as a function of population or built-up area characteristics. Step-by-Step Solution: Identify the intent: pick a widely known empirical fire demand relationship.Among common choices, the Underwriters formula is a benchmark reference in many manuals and exam contexts.Select Underwriters formula as the best answer to the phrasing “commonly cited”. Verification / Alternative check: Textbooks on water supply engineering routinely describe multiple formulas but frequently demonstrate examples using the Underwriters expression due to its prevalence in older North American standards and its conservative nature. Why Other Options Are Wrong: Kuichling's and Freeman formulas are also used but are less universally referenced in many foundational examples compared with Underwriters. Buston's formula appears in some references but is less common in standard design problems. “None of these” is incorrect because recognized formulas do exist. Common Pitfalls: Treating any single empirical formula as universally applicable without checking local fire code requirements and risk assessments. Confusing the population parameter form (e.g., use of square root of population) between different formulas. Final Answer: Underwriters formula

Water Supply Engineering Questions