3.1 Water Quality Indicators (W01) & Drinking Water Quality (W02)
Key Takeaways
- W01 Water Quality Indicators is a precondition covering all water intended for human contact - drinking, cooking, dishwashing, handwashing, showering or bathing - requiring turbidity at or below 1.0 NTU and no coliforms detected in any 100 ml sample.
- W02 Drinking Water Quality is a precondition requiring at least one drinking water dispenser plus one per dwelling unit, and sets health-based chemical limits at every dispenser.
- The W02 metal limits are arsenic 0.01, cadmium 0.003, chromium 0.05, copper 2, lead 0.01, mercury 0.006 and nickel 0.07 mg/L.
- W02 also limits nitrate to 50 mg/L as nitrate (11 mg/L as nitrogen), nitrite to 3 mg/L as nitrite (0.9 mg/L as nitrogen), fluoride to 1.5 mg/L, total chlorine to 5 mg/L and residual free chlorine to 4 mg/L.
- W02 Part 2 requires either a municipal water quality report issued within a year of registration covering at least two listed pesticides and three listed organic contaminants, or equivalent on-site testing by a professional with no conflict of interest.
3.1 Water Quality Indicators (W01) & Drinking Water Quality (W02)
Core Exam Takeaway: Get the official titles right. W01 is "Water Quality Indicators" — turbidity and coliforms, for all water intended for human contact. W02 is "Drinking Water Quality" — health-based chemical thresholds at drinking water dispensers. Water is worth 9 scored exam questions, and W01/W02 numbers are among the most directly testable facts in the entire standard.
The Water concept has three preconditions (W01, W02, W03) and five optimizations (W04–W08). There is also a beta feature, W09 Onsite Non-Potable Water Reuse; beta features are not assessable on the WELL AP exam, which is worth knowing so you do not waste study time on them.
Why water quality is a health question
Water is roughly 60% of adult body mass, and the digestive and urinary systems are the physiological pathways WELL targets in this concept. Contaminated drinking water carries chemical and microbial risk; excess moisture in buildings carries microbial risk of a different kind. WELL splits those into the threshold features here and the moisture features in W07.
Feature W01: Water Quality Indicators — Precondition
W01's intent is to verify the quality of water for human contact through easy-to-test parameters.
W01 Part 1 — Verify Water Quality Indicators
Scope is broad: water delivered to the project and intended for human contact — explicitly including drinking, cooking and dishwashing, handwashing, showering or bathing — meets:
- (a) Turbidity ≤ 1.0 NTU, FTU or FNU (nephelometric turbidity, formazin turbidity or formazin nephelometric units respectively).
- (b) Coliforms are not detected in any 100 ml sample.
Multifamily note: projects may achieve Bronze or Silver without testing in dwelling units, but cannot achieve Gold or Platinum without it. WELL Core guidance: whole building.
[!TIP] W01's two parameters are chosen because they are cheap, fast and field-testable — turbidity by nephelometer, coliforms by culture. Turbidity is also a proxy: suspended solids shield microorganisms from disinfection and indicate distribution-system disturbance, which is why a single turbidity number can gate an entire precondition.
Feature W02: Drinking Water Quality — Precondition
W02's intent is to provide access to drinking water that complies with health-based limits on chemical composition.
W02 Part 1 — Meet Chemical Thresholds
(a) Dispenser provision: the project provides at least one drinking water dispenser, plus one drinking water dispenser per dwelling unit.
(b) Health-based thresholds at all drinking water dispensers:
| Parameter | W02 threshold | Why it matters |
|---|---|---|
| Arsenic | ≤ 0.01 mg/L | Group 1 carcinogen; skin, bladder and lung cancer risk |
| Cadmium | ≤ 0.003 mg/L | Renal tubular damage, bone demineralization |
| Chromium (total) | ≤ 0.05 mg/L | Hexavalent chromium is carcinogenic |
| Copper | ≤ 2 mg/L | Gastrointestinal distress; hepatic accumulation |
| Fluoride | ≤ 1.5 mg/L | Dental and skeletal fluorosis above threshold |
| Lead | ≤ 0.01 mg/L | Irreversible neurodevelopmental harm; no safe level |
| Mercury (total) | ≤ 0.006 mg/L | Neurotoxicity, renal damage |
| Nickel | ≤ 0.07 mg/L | Dermal sensitization, allergic contact dermatitis |
| Nitrate | ≤ 50 mg/L as nitrate (11 mg/L as nitrogen) | Infant methemoglobinemia ("blue baby syndrome") |
| Nitrite | ≤ 3 mg/L as nitrite (0.9 mg/L as nitrogen) | Same mechanism, far more potent per unit |
| Total chlorine | ≤ 5 mg/L | Taste, odor and DBP precursor load |
(c) Disinfectant and disinfection byproduct thresholds at all dispensers:
- Residual (free) chlorine does not exceed 4 mg/L.
- Total trihalomethanes (TTHM — the sum of dibromochloromethane, bromodichloromethane, chloroform and bromoform**) ≤ 0.08 mg/L**.
- Haloacetic acids (HAA5 — the sum of chloroacetic, dichloroacetic, trichloroacetic, bromoacetic and dibromoacetic acids**) ≤ 0.06 mg/L**.
[!IMPORTANT] Two chlorine numbers, two meanings. W02 caps total chlorine at 5 mg/L (Part 1b) and residual free chlorine at 4 mg/L (Part 1c). A third, tighter number lives in W04 Enhanced Water Quality: free chlorine ≤ 1.25 mg/L — an aesthetic limit, because chlorine taste is the most common complaint about safe water. Three chlorine thresholds across two features is a classic exam trap.
[!IMPORTANT] Nitrate is expressed two ways. WELL states 50 mg/L as nitrate and 11 mg/L as nitrogen — the same concentration in different reporting conventions (the nitrate ion is about 4.43× the mass of its nitrogen atom). If a lab report gives "nitrate-N," compare it to 11, not 50.
W02 Part 2 — Meet Thresholds for Organics and Pesticides
Option 1: Drinking water quality report.
- (a) A municipal water quality report issued not more than one year before project registration covers at least two of the eight listed pesticides, all complying with: aldrin and dieldrin combined 0.00003; atrazine 0.1; carbofuran 0.007; chlordane 0.0002; 2,4-D 0.03; DDT and metabolites 0.001; lindane 0.002; pentachlorophenol 0.009 mg/L.
- (b) The same report contains concentrations of at least three of the ten listed organic contaminants, all complying with: benzene 0.01; benzo[a]pyrene 0.0007; carbon tetrachloride 0.004; 1,2-dichloroethane 0.03; tetrachloroethene 0.04; toluene 0.7; trichloroethene 0.02; 2,4,6-trichlorophenol 0.2; vinyl chloride 0.0003; xylenes 0.5 mg/L.
Option 2: On-site testing. All drinking water dispensers provide water meeting thresholds for at least two pesticides and three organic contaminants from the same lists, tested by a professional demonstrated not to have a conflict of interest with the WELL project.
[!TIP] The project must select pesticides and/or organic contaminants found above thresholds in any applicable municipal report, if one is available — you cannot cherry-pick the two easiest analytes while ignoring a known exceedance.
WELL Core guidance for W02: meet in the whole building. Water is sampled from non-leased spaces, and the project must either confirm the same water treatment system will be used in all leased spaces, or provide an allowance to tenants to purchase the same type of treatment system. If there is no water supply in non-leased spaces, water is sampled from leased spaces.
Reading the thresholds against regulatory benchmarks
| Parameter | WELL W02 | U.S. EPA benchmark | Comment |
|---|---|---|---|
| Lead | 0.01 mg/L | 0.015 mg/L action level | WELL is stricter and expresses it as a threshold, not an action level |
| Arsenic | 0.01 mg/L | 0.010 mg/L MCL | Aligned |
| Copper | 2 mg/L | 1.3 mg/L action level | WELL's health limit is looser than EPA's action level, but W04's aesthetic limit of 1 mg/L is tighter |
| TTHM | 0.08 mg/L | 0.080 mg/L MCL | Aligned |
| HAA5 | 0.06 mg/L | 0.060 mg/L MCL | Aligned |
The pattern matters more than any single row: WELL adopts WHO and EPA health-based values where they exist, tightens where evidence supports it (lead), and adds a separate aesthetic layer in W04 for parameters that drive people to sugary drinks instead of water.
Under WELL v2 Feature W01, which water does the turbidity and coliform requirement apply to?
Which pairing of contaminant and WELL v2 Feature W02 threshold is correct?
A project wants to satisfy W02 Part 2 using a municipal water quality report. What must the report demonstrate?
A project's drinking water tests at 4.6 mg/L total chlorine and 3.8 mg/L residual free chlorine. Does it meet WELL v2 Feature W02?