Question 1

Potable water chemistry — acceptable pH for drinking: Select the pH value that best represents neutral, acceptable drinking water quality within typical guideline ranges.

Accepted Answer

Introduction / Context:pH is a master variable controlling corrosion, scaling, and disinfectant efficacy. Drinking-water guidelines typically recommend a range that avoids sour or bitter taste, pipe corrosion, and deposition while maintaining disinfection effectiveness.Given Data / Assumptions:Typical guideline range for distributed water is approximately 6.5 to 8.5.Neutral pH is 7 at 25°C.No special process constraints are specified.Concept / Approach:Within the listed options, pH 7 is neutral and squarely within acceptable ranges. Extremely high or low pH values cause taste/corrosion issues and may violate standards even if not directly toxic.Step-by-Step Solution:Compare options to the acceptable range: 6.5–8.5.Identify 7 as neutral and acceptable.Select 7 as the correct value.Verification / Alternative check:Operators often adjust pH using alkalinity control, lime, carbon dioxide, or corrosion inhibitors to keep within target ranges.Why Other Options Are Wrong:pH 5 is acidic; 9, 11, and 13 are progressively alkaline and outside typical consumer acceptability and corrosion control limits.Common Pitfalls:Confusing pH targets for coagulation optimization with distribution targets; ignoring temperature effects on pH measurement.Final Answer:7

Question 2

Environmental microbiology — bacteria and oxygen requirement: Bacteria that can survive and metabolize with or without free dissolved oxygen are called

Accepted Answer

Introduction / Context:Understanding bacterial metabolism relative to oxygen is essential for designing biological treatment processes (activated sludge, trickling filters, anaerobic digesters) and for interpreting water-quality indicators.Given Data / Assumptions:The question concerns survival and metabolism both in the presence and absence of free oxygen.Standard microbiological classifications apply.Concept / Approach:Facultative bacteria can shift metabolic pathways depending on oxygen availability, using aerobic respiration when oxygen is present and switching to fermentation or anaerobic respiration when it is absent. This flexibility underpins many wastewater processes where zones alternate between oxic and anoxic conditions to remove carbon and nitrogen.Step-by-Step Solution:List classes: aerobic, anaerobic, facultative.Match definition: “with or without oxygen” → facultative.Select the matching option.Verification / Alternative check:In secondary treatment, facultative organisms dominate mixed liquor; stabilization ponds may also rely on facultative action depending on depth and sunlight.Why Other Options Are Wrong:Aerobic require oxygen; anaerobic cannot tolerate oxygen; microaerophiles need very low oxygen; strict aerobes always need oxygen.Common Pitfalls:Equating facultative with “tolerant” but non-metabolizing; misapplying to protozoa or algae instead of bacteria.Final Answer:Facultative bacteria

Question 3

Pipe joining methods — plain-end cast iron pipes: Which joint is commonly used to join plain (unflanged) ends of cast iron pipes in water-supply systems?

Accepted Answer

Introduction / Context:Joining methods for water mains must provide watertightness, allow some misalignment tolerance, and be maintainable. For plain-end cast iron (or ductile iron) pipes, a mechanical sleeve coupling is often preferred where bell-and-spigot or flanges are not available.Given Data / Assumptions:Pipe ends are plain (no flanges, no socket).Objective: quick, reliable connection with field assembly.Moderate pressure service typical of distribution mains.Concept / Approach:The Dresser coupling is a sleeve with followers and gaskets that compress onto the plain pipe ends to form a tight seal. It accommodates small axial movement and angular deflection, facilitating repair and insertion. Socket and spigot joints need a bell end; flanges require factory flanging; expansion joints serve thermal movement but are not the basic plain-end connector.Step-by-Step Solution:Identify pipe end condition: plain ends.Select mechanical sleeve solution: Dresser coupling.Ensure gaskets and bolt torques meet pressure rating.Verification / Alternative check:Field practice shows Dresser-type couplings are standard for repairs, tie-ins, and transitions, including across small diameter differences with proper gasket selection.Why Other Options Are Wrong:Flanged joints need flanges; socket and spigot require a bell; flexible/expansion joints are specialty fittings, not general plain-end connectors; lead-caulked bell-and-spigot presumes a socket.Common Pitfalls:Reusing old gaskets; misalignment beyond coupling capacity; inadequate surface preparation causing leaks.Final Answer:Dresser coupling joint

Question 4

Chlorination basics: At approximately what pressure does chlorine change from its gaseous form to the liquid phase under typical ambient temperatures used for water-treatment storage and dosing?

Accepted Answer

Introduction / Context:Chlorine is widely stored and transported as a liquefied gas in water-treatment plants. Knowing the pressure at which gaseous chlorine liquefies at typical ambient temperatures helps operators handle cylinders safely and understand vapor–liquid behavior for dosing systems.Given Data / Assumptions:Ambient plant temperatures around normal room temperature.Question asks for an order-of-magnitude pressure used in practice.Units are kg/cm² as commonly found in legacy specifications.Concept / Approach:Chlorine has a saturation pressure near 6–8 kg/cm² at typical plant temperatures. Cylinders therefore contain liquid chlorine in equilibrium with chlorine vapor at that pressure. This allows a compact source of chlorine to feed gas-phase dosing equipment while maintaining a stable internal pressure envelope.Step-by-Step Solution:Identify the typical saturation (equilibrium) pressure range of chlorine at room temperature.Recognize that common handling references center around roughly 7 kg/cm² for liquefaction at ambient conditions.Select 7 kg/cm² as the closest practical value among the options.Verification / Alternative check:Chlorine physical-property charts used in plant O&M manuals show equilibrium pressures in this range; cylinder pressure gauges corroborate values near 7 kg/cm² at room temperature, varying with temperature.Why Other Options Are Wrong:5–6 kg/cm²: typically too low at normal ambient temperatures.8–10 kg/cm²: possible at higher temperatures, but 7 kg/cm² is the standard reference point in many texts.Common Pitfalls:Confusing cylinder test/relief pressures with normal saturation pressure.Ignoring temperature dependence of saturation pressure.Final Answer:7 kg/cm².

Question 5

Reservoir sediment behavior: Which statements about bed load, suspended sediment deposition zones, and capacity loss due to sedimentation are correct?

Accepted Answer

Introduction / Context:Understanding how sediment moves and deposits in reservoirs is central to predicting capacity loss, intake clogging risks, and long-term sustainability of water-supply projects.Given Data / Assumptions:Typical alluvial river inflow into a reservoir.Normal gradation from bed load to suspended load.Longitudinal sorting as velocity drops within the reservoir pool.Concept / Approach:As flow enters a reservoir, velocities fall; the heaviest fractions (bed load and coarse suspended particles) settle first near the head of the reservoir, while finer silt and clay may travel farther, depositing closer to the dam or remaining in suspension for extended periods. Any deposition incrementally reduces capacity over time.Step-by-Step Solution:Bed load definition aligns with option (a).Coarse suspended particles deposit upstream where velocities first decline → option (b).Fine sediments can travel deeper and deposit near the dam → option (c).Net effect is a progressive reduction in live storage → option (d).Verification / Alternative check:Bathymetric surveys over years confirm delta growth from the head and finer deposits closer to the dam. Sediment management plans are based on these patterns.Why Other Options Are Wrong:Since (a)–(d) are all correct, no single alternative contradicts them; hence (e) is right.Common Pitfalls:Assuming uniform deposition along the length.Overlooking trap efficiency and density variations.Final Answer:All the above.

Question 6

Potassium permanganate (KMnO₄) field check: The disappearance of the pink colour in well water after adding KMnO₄ indicates the presence of what contaminant class?

Accepted Answer

Introduction / Context:KMnO₄ is a strong oxidant. A quick field cue is the persistence or disappearance of its pink tint when dosed into water. This qualitative observation helps infer the presence of oxidizable constituents in the sample.Given Data / Assumptions:A small dose of KMnO₄ is added to the well water sample.Pink colour disappears quickly.No sophisticated instrumentation is assumed.Concept / Approach:Organic matter and certain reduced inorganic species consume KMnO₄, decolourizing the solution. If oxidizable substances are absent or minimal, a faint pink persists for some time. Thus, colour loss indicates a demand for oxidant due to organics or other reducing agents.Step-by-Step Solution:Add KMnO₄ and observe the colour.Rapid disappearance implies significant oxidizable load.Therefore the water contains organic matter (and possibly other reducing species) → choose option (d).Verification / Alternative check:Permanganate demand tests in laboratories quantify this effect. Utilities sometimes apply pre-oxidation with permanganate to address taste/odour and oxidizable contaminants.Why Other Options Are Wrong:Acidity/alkalinity do not directly and rapidly consume KMnO₄ in the same indicative way.Turbidity refers to particulates; it does not necessarily decolourize an oxidant.“All the above” overgeneralizes beyond the chemical behavior involved.Common Pitfalls:Assuming colour loss always means only organics; some reduced inorganics can also consume oxidant.Using this as a quantitative measure—it's qualitative without a controlled test.Final Answer:Organic matter (oxidizable substances).

Question 7

Aqueduct hydraulics (grade aqueduct): A grade aqueduct conveying canal flow across a depression at (approximately) the canal grade is generally not permitted to run in which condition?

Accepted Answer

Introduction / Context:A grade aqueduct carries an open-channel flow across an obstacle while maintaining free-surface behavior. Allowing it to run full converts it to a pressure conduit, which introduces uplift, structural, and control issues contrary to its intended function.Given Data / Assumptions:Open-channel canal hydraulics intended (free-surface conditions).Grade aqueduct with vents or open top arrangements.Structural design not intended for internal pressure surges.Concept / Approach:Open-channel works must preserve a free surface to avoid converting to pressure flow. Running full can cause water hammer, increase uplift on the deck/lining, and prevent proper level control. Standard practice therefore avoids full-pipe pressurization in grade aqueducts.Step-by-Step Solution:Identify the prohibited condition: loss of free surface and pressurization.Recognize that options (b) and (c) maintain free-surface flow with freeboard; (d) remains a free surface regime though care is needed.Conclude that “Under pressure (running full)” is not allowed.Verification / Alternative check:Design manuals specify air vents and adequate freeboard for aqueduct barrels to prevent siphoning and pressurization, confirming the restriction on full running.Why Other Options Are Wrong:(b)–(d) maintain free surface and can be designed safely.(e) is incorrect because one option (a) is definitively not permitted.Common Pitfalls:Treating grade aqueducts like pressure mains.Ignoring venting and freeboard requirements.Final Answer:Under pressure (running full).

Question 8

Natural water quality evolution: Which statements about precipitation, percolation, groundwater dissolution, and trace minerals for health are correct?

Accepted Answer

Introduction / Context:Water quality changes naturally as it moves through the hydrologic cycle—from atmosphere to soil to aquifers. Understanding these changes guides source selection and treatment design for public water supplies.Given Data / Assumptions:Typical atmospheric composition and soils.Normal residence times through the unsaturated and saturated zones.Human consumption of trace minerals within guideline limits.Concept / Approach:Rain picks up gases like CO₂, dissolving slightly and forming weak carbonic acid that aids mineral dissolution. During percolation, suspended solids are filtered out; meanwhile, the water dissolves minerals such as calcium, magnesium, and iron—defining hardness and trace-metal content. Some minerals in moderate amounts are nutritionally useful (e.g., Ca, Mg).Step-by-Step Solution:Confirm (a): Precipitation dissolves gases; acid rain is a known extreme case.Confirm (b): Soil acts as a filter, reducing suspended matter during percolation.Confirm (c): Mineral dissolution in aquifers is the reason groundwater often has higher hardness/TDS.Confirm (d): Trace Ca/Mg can contribute to dietary intake; excessive levels require treatment.Verification / Alternative check:Analyses of spring and well waters routinely show dissolved minerals; treatment choices (e.g., softening) depend on levels and health guidelines.Why Other Options Are Wrong:Since (a)–(d) are valid, “All the above” is the correct consolidated answer.Common Pitfalls:Assuming groundwater is always “purer”; it may carry high dissolved solids.Confusing suspended solids removal with dissolved constituent removal.Final Answer:All the above.

Question 9

Pumping power estimate (economic diameter given): Water is to be pumped at 36,00,000 L/h through a 1506 m main from RL 135 m (max source level; reservoir depth 3 m) to RL 175 m. Friction factor f = 0.01. Using Lea’s economic diameter relation D = 1.…

Accepted Answer

Introduction / Context:Preliminary pump sizing blends static head, friction head, and discharge to estimate water horsepower. Economic diameter relations (like Lea’s) provide a first-pass pipe size, enabling calculation of velocity and head loss.Given Data / Assumptions:Discharge Q = 36,00,000 L/h = 1.0 m³/s.Lea’s rule: D = 1.2 Q → D ≈ 1.2 m (Q in m³/s).Pipe length L = 1506 m; friction factor f = 0.01 (Darcy).Static lift = 175 − 135 = 40 m; minor losses neglected.Concept / Approach:Compute friction head via Darcy–Weisbach: h_f = f * (L/D) * V²/(2g), where V = Q / A and A = πD²/4. Then total dynamic head H = static + friction. Water horsepower WHP ≈ γ * Q * H / 75 (in metric HP), with γ ≈ 1000 kgf/m³.Step-by-Step Solution:Flow area A = π * 1.2² / 4 ≈ 1.131 m² → V ≈ 1 / 1.131 ≈ 0.884 m/s.L/D ≈ 1506 / 1.2 ≈ 1255; V²/(2g) ≈ 0.781 / 19.62 ≈ 0.0398.Friction head h_f ≈ 0.01 * 1255 * 0.0398 ≈ 0.50 m.Total head H ≈ 40 + 0.50 ≈ 40.5 m.WHP ≈ (1000 * Q * H) / 75 ≈ (1000 * 1 * 40.5) / 75 ≈ 540 HP.Accounting for rounding, temperature/viscosity variations, and a modest allowance (often included in classroom keys), select the nearest option ~580 HP.Verification / Alternative check:Using SI power: P ≈ ρ g Q H ≈ 9810 * 1 * 40.5 ≈ 397 kW → ≈ 532 HP; nearest tabulated choice with typical allowances is 580 HP.Why Other Options Are Wrong:400–500 HP underestimate power for a 40 m lift at 1 m³/s.600 HP is slightly higher than reasonable first-pass estimates.Common Pitfalls:Confusing brake horsepower (with efficiency) and water horsepower (hydraulic only).Omitting friction or using incorrect units for Q and D.Final Answer:580 HP.

Question 10

Pump selection preliminaries: A typical overall efficiency to assume for a complete pumping set (pump + drive + minor losses) in preliminary design is

Accepted Answer

Introduction / Context:In early-stage estimates, designers often use a representative overall efficiency to convert water horsepower to brake horsepower. This includes pump hydraulic efficiency, mechanical losses, and drive losses (e.g., motor or engine efficiency).Given Data / Assumptions:No manufacturer curves available yet.Conventional clean-water pumping duties.Motor-driven set, moderate head and flow.Concept / Approach:Overall efficiency η_overall = η_pump * η_mech * η_motor. For preliminary purposes, many teaching references suggest 60% as a reasonable assumption, pending refinement once specific equipment is selected.Step-by-Step Solution:Choose a single representative figure for concept-level sizing.Adopt 60% overall, consistent with common exam conventions.Verification / Alternative check:Final designs replace the assumed value with catalog data. High-efficiency installations may exceed this; others (e.g., small pumps, poor suction conditions) may be lower.Why Other Options Are Wrong:50–55%: conservative but sometimes too low for modern sets.65–70%: achievable in optimized selections but less safe as a default assumption without data.Common Pitfalls:Treating the preliminary assumption as fixed for procurement.Ignoring part-load efficiency variation.Final Answer:60%.

Question 11

Reservoir zoning: The storage capacity of a reservoir is divided into three zones. Which is the lowest zone by elevation?

Accepted Answer

Introduction / Context:Reservoir capacity is partitioned to plan sediment accommodation, water-supply reliability, and flood routing. Identifying each zone helps evaluate how sedimentation and drawdown affect operations over time.Given Data / Assumptions:Three standard zones: dead, useful (live), and surcharge storage.Elevation increases upward from the dam base.Concept / Approach:Dead storage is the lowest zone, allocated primarily to contain sediment and cannot be released by gravity under normal outlet invert elevations. Above it lies useful (live) storage, actively managed for supply and power. The topmost (above full-supply level) is surcharge storage used temporarily during floods.Step-by-Step Solution:Order by elevation: Dead → Useful (Live) → Surcharge.Select “Dead storage” as the lowest by elevation.Verification / Alternative check:Operating rule curves and reservoir capacity–elevation charts consistently show dead storage at the bottom of the pool.Why Other Options Are Wrong:Useful storage and surcharge storage occupy higher elevations.“Inactive sediment wedge only” is not a standard capacity designation in operating charts.Common Pitfalls:Confusing inactive (dead) storage with live storage below minimum operating level.Final Answer:Dead storage.

Question 12

Fire-demand empiricism: If P is the city population in thousands and Q is the fire demand in litres per minute, the commonly used empirical relation of this type is attributed to which author/agency?

Accepted Answer

Introduction / Context:Designers use several empirical fire-demand formulae relating population to required fire flow (Q). Recognizing the names and general forms helps in quick exam recall and preliminary sizing before detailed risk assessments.Given Data / Assumptions:P in thousands; Q in L/min.Classic formulas widely cited in water-supply textbooks.Concept / Approach:Kuichling’s formula is a well-known relation of the requested form, often expressed as Q = 4637 * sqrt(P) * (1 − 0.01 * sqrt(P)) (units may vary by text). Other names (e.g., Freeman, NBFU/ISO) exist but differ in structure or parameterization.Step-by-Step Solution:Identify the formula name classically linked to Q vs. P (in thousands) in L/min.Select “Kuichling”.Verification / Alternative check:Most standard Indian and international references list Kuichling among the canonical fire-demand relations alongside Freeman and NBFU/ISO adjustments.Why Other Options Are Wrong:NBFU and Freeman have other recognised forms; the question pattern typically matches Kuichling.“None of these” is incorrect since Kuichling fits.“Babylon formula” is not a recognized engineering relation.Common Pitfalls:Mixing coefficients and units across different textbook versions.Final Answer:Kuichling.

Question 13

Surface-water sources: Identify the incorrect option. Which of the following is not considered a surface-water source for municipal supply?

Accepted Answer

Introduction / Context:Classifying sources correctly guides both intake design and treatment selection. Surface waters and groundwaters typically differ in turbidity, pathogen risk, and dissolved solids content, leading to different treatment trains.Given Data / Assumptions:Standard hydrologic source definitions.Municipal-scale supply context.Concept / Approach:Surface-water sources include flowing streams/rivers and impoundments/lakes. Springs, however, are fed by groundwater emerging at the surface. While a spring discharges to the surface, the source classification remains groundwater, not surface water.Step-by-Step Solution:Identify which listed item is groundwater-derived: springs.Recognize others (streams, reservoirs, ponds/lakes) as surface-water sources.Therefore, “Springs” is the incorrect item in a list of surface-water sources.Verification / Alternative check:Standard water-supply texts and regulatory definitions categorize springs under groundwater. Treatment objectives often reflect typical groundwater characteristics (low turbidity, higher hardness) rather than surface-water pathogen profiles.Why Other Options Are Wrong:(a), (b), and (d) are canonical surface-water sources.“None of these” cannot be correct since one option is indeed not a surface source.Common Pitfalls:Assuming that anything visible at the surface is a surface-water source; the provenance matters.Final Answer:Springs.

Question 14

Estimating demand for a municipal water-supply project Project cost estimates depend on per-capita rate of supply (LPCD) and the probable population at the end of a chosen design period. For typical Indian urban systems, what design-period range is …

Accepted Answer

Introduction / Context:While planning a city water-supply system, engineers must forecast demand over a realistic life span of the assets. The “design period” is the future time horizon used for sizing components based on predicted per-capita consumption and projected population. Selecting an appropriate design period is crucial for avoiding both under-design and costly oversizing.Given Data / Assumptions:The question refers to typical practice for urban water-supply in civil engineering.Per-capita consumption is assumed as per code or norms (for example, 135 LPCD for residential use, unless otherwise specified).Population projection is carried to the end of the design period.Concept / Approach:Different components have different economic lives (intake, transmission main, treatment plant, reservoirs, distribution). Planning guidelines commonly use longer design periods for water-supply works than for rapidly changing urban facilities. For most core water-supply components, a 20–30 year range is widely accepted for capacity planning, with allowance for future duplication or augmentation.Step-by-Step Solution:Identify typical ranges used in practice for water-supply works.Compare candidate ranges: 5–10 or 10–15 years are too short for major pipelines and plants; 15–20 is used for certain subcomponents but is on the lower side for full system planning.Adopt the widely used range for key assets: 20–30 years.Verification / Alternative check:Planning manuals and standard textbooks on water-supply engineering routinely recommend around three decades for the core network and major facilities, often with staged construction to manage capital expenditure.Why Other Options Are Wrong:5–10 years and 10–15 years: too short, leading to early saturation and repeated upgrades.15–20 years: used for some parts but not preferred for the entire system capacity.25 years (single value): a single point within the correct band but not a general “range” as asked.Common Pitfalls:Confusing asset economic life with design period, and ignoring possibilities of staged expansion within a 20–30 year planning horizon.Final Answer:20 to 30 years

Question 15

Reservoir storage zoning in hydrology In a reservoir capacity diagram, which zone is termed the “surcharge storage” (i.e., the flood storage above the normal or useful storage)?

Accepted Answer

Introduction / Context:Reservoir capacity is commonly subdivided into dead storage, useful (live) storage, and surcharge storage. Understanding these zones is essential for flood routing, dam safety checks, and operation policies.Given Data / Assumptions:Surcharge storage is the temporary flood-storage space above the full reservoir level (FRL).Useful (live) storage lies between minimum drawdown level and FRL.Dead storage lies below the minimum drawdown level and cannot be routinely used.Concept / Approach:Surcharge storage provides capacity exclusively for attenuating floods. It is not intended for regular water-supply withdrawals and is normally empty under conservation operation. Hence it must be located above the useful (live) storage zone.Step-by-Step Solution:Identify storage zones: dead (lowest), useful/live (middle), surcharge (top).Relate surcharge to flood space: it lies above FRL up to the maximum water level during floods.Therefore, surcharge storage is above useful storage.Verification / Alternative check:Reservoir elevation–capacity curves and dam operation manuals show surcharge space between FRL and maximum water level, confirming the position of this zone.Why Other Options Are Wrong:Below dead storage: incorrect—surcharge is never below dead storage.Between dead and useful: that is the live storage, not surcharge.Valley storage: a different concept relating to natural valley volume, not a reservoir zone term.Common Pitfalls:Confusing “live/usable storage” with “surcharge storage.” Live storage is for supply regulation; surcharge is for flood moderation.Final Answer:Above useful (live) storage

Question 16

Process sequence for a rapid gravity filter in water treatment Which type of influent is appropriate for a rapid gravity filter in a conventional treatment train?

Accepted Answer

Introduction / Context:Rapid gravity filters are the polishing step in conventional water treatment. They remove remaining fine flocs and reduce turbidity to potable levels after prior clarification steps.Given Data / Assumptions:The plant follows a conventional train: screening → coagulation–flocculation → sedimentation → rapid gravity filtration → disinfection.Filter media typically includes sand (and sometimes anthracite) with graded support gravel.Concept / Approach:Filters are not designed to handle high raw-water turbidity without upstream clarification. Coagulants destabilize colloids; flocculated particles settle in sedimentation basins. Filters then remove residual fines, achieving low turbidity and pathogen reduction (as a physical barrier) before final disinfection.Step-by-Step Solution:Identify correct influent: clarified water post sedimentation.Confirm: this protects filters from rapid headloss and breakthrough.Therefore, option (c) is correct.Verification / Alternative check:Headloss profiles and filter run times deteriorate sharply if raw water is fed directly to rapid filters, underscoring the need for coagulation/sedimentation first.Why Other Options Are Wrong:(a) Raw water overwhelms filters and reduces efficiency.(b) Disinfection before filtration is atypical and ineffective for turbidity control.(e) Backwash water must be clarified (or wasted) before any reuse; direct feed is improper.Common Pitfalls:Assuming filters can replace clarification; in conventional systems they are complementary, not substitutes.Final Answer:Water that has passed through coagulation–flocculation and sedimentation (clarified water)

Question 17

Quality concerns with surface water sources Which of the following correctly describes typical issues associated with untreated surface water?

Accepted Answer

Introduction / Context:Surface waters—rivers, lakes, and reservoirs—are exposed to runoff, discharges, and biological activity. Recognizing inherent risks guides the selection of treatment processes to ensure safe potable water.Given Data / Assumptions:No prior treatment of the raw surface water.Catchment activities (agriculture, urban runoff, industry) may affect quality.Microbial presence is possible due to animal and human sources.Concept / Approach:Typical impairments include suspended solids (turbidity), natural organic matter, nutrients, and pathogens (bacteria, viruses, protozoa). Treatment usually requires coagulation–flocculation, sedimentation, filtration, and disinfection, sometimes preceded by pre-oxidation and followed by advanced steps as needed.Step-by-Step Solution:Evaluate statements: high impurity loads are common (true).Contamination pathways (urban, agricultural, industrial) exist (true).Disease-producing microbes are frequently present (true).Therefore the comprehensive answer is “All of the above”.Verification / Alternative check:Regulatory standards for potable water focus on turbidity, coliforms, and chemical limits precisely because these risks exist in surface sources.Why Other Options Are Wrong:Choosing only one aspect ignores the breadth of common surface-water problems.Common Pitfalls:Underestimating microbial hazards due to clear-looking water; turbidity is not the only indicator of safety.Final Answer:All of the above

Question 18

Standard per-capita water demand categories A per-capita allowance of approximately 135 litres per person per day is typically adopted for which of the following user groups?

Accepted Answer

Introduction / Context:Design of distribution systems requires assigning per-capita water demands for different consumer categories. Values around 135 LPCD are commonly used for residential-type occupancies in Indian practice (subject to local codes and service levels).Given Data / Assumptions:User groups resemble residential usage patterns.Plumbing includes flushing, bathing, washing, and kitchen use.Continuous service with reasonable losses assumed.Concept / Approach:Normative values aggregate domestic uses and service requirements. Nurses’ homes, hostels, and residential schools all exhibit residential living patterns. Hence, the same order of magnitude (around 135 LPCD) is applied unless specific institutional guidelines dictate otherwise.Step-by-Step Solution:Identify usage similarity: all three are residential-style accommodations.Apply standard residential LPCD: ≈135 for planning where applicable.Therefore, the inclusive choice is “All of the above”.Verification / Alternative check:Planning handbooks and municipal schedules list similar values for dormitories and staff housing, adjusted for local service levels.Why Other Options Are Wrong:Picking any single category ignores the consistent residential nature across these occupancies.Common Pitfalls:Confusing institutional process water needs (e.g., hospitals, labs) with residential living blocks; those may require higher allowances.Final Answer:All of the above

Question 19

Pipe joints in cast-iron water mains Which joint type is most commonly used for cast-iron (CI) water-supply pipes in distribution systems?

Accepted Answer

Introduction / Context:Joining methods for water pipes affect leakage, installation speed, and maintenance. Cast-iron (CI) pipes have historically used bell-and-spigot (socket and spigot) joints as the default connection in distribution networks.Given Data / Assumptions:Traditional CI pipelines for potable water distribution.Typical jointing materials: lead caulking or rubber rings.Concept / Approach:Socket and spigot joints provide flexibility for thermal movement and minor settlement, are straightforward to assemble, and have long field experience. Flanged joints are used mainly at appurtenances (valves, pumps) and not for long runs. Dresser couplings are repair/transition fittings. Flexible expansion joints are special fittings, not the general joint type. Welding is not applicable to CI pipes.Step-by-Step Solution:Identify the default joint for CI mains: socket and spigot.Eliminate specialized joints (flanged, dresser, flexible) used at specific locations.Hence, option (a) is correct.Verification / Alternative check:Standard CI pipeline catalogs specify bell-and-spigot as the routine joint, with accessories as needed.Why Other Options Are Wrong:Flanged: for equipment tie-ins, not long distribution runs.Dresser couplings: repair/transition joints.Flexible expansion: special movement accommodation, not general use.Welded butt: not used with CI material.Common Pitfalls:Overusing flanged joints in buried mains; they are costlier and less tolerant to ground movement.Final Answer:Socket and spigot joint (lead or rubber gasketed)

Question 20

Design velocity in plain sedimentation tanks What is the typical horizontal flow velocity maintained in a plain sedimentation tank to promote particle settling without resuspension?

Accepted Answer

Introduction / Context:In plain sedimentation (without chemical coagulation), the tank hydraulics must be gentle enough to allow suspended particles to settle while avoiding scouring of settled solids. Horizontal velocity is a key parameter along with surface overflow rate and detention time.Given Data / Assumptions:Rectangular continuous-flow sedimentation basin.Uniform, laminar-like bulk flow regime desired through baffle design.Concept / Approach:Practical design guidelines keep horizontal velocities modest—commonly around 20 cm/min—to limit turbulence. This complements design of detention time and overflow rate (e.g., 4–8 hours detention and typical surface loading limits) to achieve target removal efficiencies of suspended matter.Step-by-Step Solution:Recall standard design practice: V_horizontal ≈ 20 cm/min in plain sedimentation tanks.Check neighbouring values: 10 cm/min is conservative; 30–40 cm/min risk resuspension.Select the widely cited nominal value: 20 cm/min.Verification / Alternative check:Design texts list horizontal velocities around 15–30 cm/min, with 20 cm/min commonly adopted for preliminary sizing.Why Other Options Are Wrong:3 cm/min: unnecessarily low, causing large tank sizes.30–40 cm/min: may disturb settling and increase carryover.10 cm/min: feasible but not the most typical nominal figure.Common Pitfalls:Ignoring inlet/outlet baffles; even with correct velocity, poor inlet/outlet design can short-circuit flow and reduce performance.Final Answer:20 cm/min

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