Drinking water clarity benchmark: typical desirable turbidity limit For potable water acceptability in distribution, what is a commonly specified desirable turbidity (expressed in NTU; historically reported as “ppm” in some texts) used by many standards bodies?

Introduction / Context:
Turbidity is a key indicator of particulate content and aesthetic quality in drinking water. Lower turbidity improves disinfection efficacy and reduces the risk of microbial breakthrough. Although turbidity is properly measured in NTU (nephelometric turbidity units), older materials sometimes loosely refer to “ppm”; in practice, specifications are stated in NTU.

Given Data / Assumptions:

• Focus on a commonly cited “desirable” benchmark for finished water (not a relaxed upper emergency limit).
• Modern distribution systems aim for very low turbidity post-filtration.

Concept / Approach:
Many guidelines specify a desirable finished water turbidity of about 1 NTU or less at consumers’ taps, with regulatory maxima for conventional treatment typically set at or below 1 NTU in continuous monitoring and occasional short-term limits up to 5 NTU (depending on jurisdiction). Therefore, among the options, 1 is the closest and most appropriate desirable value.

Step-by-Step Solution:

Verification / Alternative check:
Plant performance data for well-operated rapid sand or membrane filtration routinely show < 0.3–1.0 NTU; many utilities set internal goals tighter than regulatory maxima to safeguard disinfection.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing “regulatory maximum” with “desirable target.” Always design and operate toward the lower, more protective figure.

Final Answer:
1