Module 01
Water Quality
Fundamentals
Estimated reading time: 8 minutes
Understanding what is in residential tap water — and why it matters — is the foundation of everything we do. This module covers the categories of water contaminants, how they affect human health, and where we source credible data.
Why Water Quality Varies
Municipal water treatment is designed to make water safe to drink under federal legal standards — not to remove every contaminant to the lowest possible health-protective level. Water quality varies by utility, infrastructure age, source water, and treatment technology.
The U.S. has over 148,000 public water systems. Roughly 70–80% of the population receives water from a community water system. The remaining population relies on private wells, which are not federally regulated for contaminant levels.
Key Principle
Legal compliance does not equal optimal health protection. The gap between what is legally permitted and what the current science considers safe is where our work begins.
The Four Contaminant Categories
EPA classifies drinking water contaminants into four primary categories. Each presents distinct risk profiles and requires different treatment approaches.
⚗️
Chemical
Pesticides, herbicides, industrial solvents, disinfection byproducts, heavy metals (lead, arsenic, chromium-6). Often invisible, odorless.
PFAS · Atrazine · Nitrates · VOCs
☢️
Radiological
Radium, radon, uranium — naturally occurring in some groundwater supplies. Linked to increased cancer risk with long-term exposure.
Radium-226/228 · Uranium
🦠
Microbial
Bacteria (E. coli, Legionella), viruses, protozoa (Giardia, Cryptosporidium). Primary target of chlorine disinfection at the utility level.
Chlorination is standard
🪨
Physical
Sediment, turbidity, total dissolved solids (TDS), hardness minerals (calcium, magnesium). Affects aesthetics, taste, and appliance longevity.
TDS · Hardness · Sediment
Contaminants of Primary Concern: Field Reference
The following are the contaminants most commonly detected above health-protective levels in U.S. residential tap water, based on EWG Tap Water Database analysis of utility-reported testing data.
| Contaminant |
Source |
Primary Health Concern |
EWG vs Legal |
| Total Trihalomethanes (TTHMs) |
Chlorination byproduct |
Increased cancer risk; reproductive effects |
Exceeds EWG guideline |
| Haloacetic Acids (HAAs) |
Chlorination byproduct |
Cancer risk; developmental effects |
Exceeds EWG guideline |
| Chromium-6 (Hexavalent) |
Industrial discharge, natural |
Carcinogen; no federal MCL specific to Cr-6 |
No federal limit for Cr-6 |
| Nitrates |
Agricultural runoff, fertilizers |
Blue baby syndrome; thyroid disruption |
Varies by region |
| Lead |
Aging pipes, solder, fixtures |
Neurological damage; no safe level for children |
EWG guideline: zero |
| PFAS (Forever Chemicals) |
Industrial use, firefighting foam |
Cancer, immune, hormonal disruption |
New EPA limits (2024) |
| Arsenic |
Natural geology, mining |
Carcinogen; skin, lung, bladder |
Exceeds EWG guideline |
| Hardness (Ca/Mg) |
Natural mineral content |
Scale buildup; appliance damage; skin/hair |
No federal standard |
Important
Lead enters water almost entirely through household plumbing — pipes, solder, and fixtures — not from the utility source. A utility can be 100% lead-compliant at the treatment plant and still deliver lead at the tap. This is why point-of-use treatment matters.
Where We Source Data
Two primary data sources inform water quality conversations in the field:
Consumer Confidence Report (CCR)
Issued by: Utility (required by EPA annually)
Measures against: Federal MCLs (legal limits)
Limitation: Legal compliance ≠ health-protective. Many MCLs are decades old.
Result: Most utilities show "passing" even with concerning contaminant levels
EWG Tap Water Database
Issued by: Environmental Working Group (independent nonprofit)
Measures against: Health-based guidelines, current science
Strength: Searchable by zip code. Compares detected levels to EWG health guidelines — often 100x stricter than legal limits.
Result: Reveals the gap between "legal" and "safe"
Field Note
In the field, always attribute data to EWG specifically — "according to the EWG Tap Water Database." This is a named, verifiable third-party source. Reps do not make claims; they reference data that the resident can verify themselves at ewg.org/tapwater.
Module 02
Legal vs. Health
Standards
Estimated reading time: 7 minutes
The single most important concept in water safety literacy is the gap between what is legally allowed and what is scientifically protective. This module defines the regulatory framework — and why compliance is not the same as safety.
The Federal Regulatory Framework
Drinking water safety in the U.S. is governed primarily by the Safe Drinking Water Act (SDWA) of 1974, enforced by the U.S. Environmental Protection Agency (EPA). The SDWA establishes two critical types of standards:
| Standard |
Full Name |
Legal Force |
Basis |
| MCLG |
Maximum Contaminant Level Goal |
Non-enforceable |
Pure health science — the level at which no known health risk exists, with adequate safety margin |
| MCL |
Maximum Contaminant Level |
Enforceable |
Set as close to the MCLG as "feasible" — balancing health with treatment cost and technology |
| TT |
Treatment Technique |
Enforceable |
Required treatment process when measuring a contaminant is not feasible (e.g., Lead and Copper Rule) |
| SMCL |
Secondary MCL |
Non-enforceable |
Aesthetic standards — taste, odor, color. No health mandate. |
Critical Gap
For many contaminants, the MCLG (health goal) is zero — meaning no safe level exists — while the enforceable MCL allows measurable concentrations. Example: Total Trihalomethanes have an MCL of 80 ppb. The EWG health guideline is 0.15 ppb. That is a 533× difference between legal and health-protective.
Why MCLs Lag Behind the Science
MCLs are not updated in real time. The EPA regulatory process is slow by design — requiring notice-and-comment rulemaking that can take years to decades. As a result:
- Many MCLs are 20–30 years old and predate modern toxicology research on compounds like PFAS, chromium-6, and certain disinfection byproducts.
- Economic feasibility is factored in. A contaminant may be scientifically linked to harm at lower concentrations, but the MCL is set at a level that utilities can affordably achieve.
- PFAS is a current example: EPA issued enforceable PFOA/PFOS limits in 2024 — the first new contaminant regulations in decades — at 4 ppt. Some states had already set stricter standards years earlier.
- California has its own standards (under the State Water Resources Control Board) that are often stricter than federal minimums — particularly for chromium-6, PFAS, and 1,2,3-TCP.
California-Specific Regulatory Context
California operates under the California Safe Drinking Water Act, administered by the State Water Resources Control Board (SWRCB) Division of Drinking Water (DDW). California sets standards independently and is frequently ahead of federal action.
| Contaminant |
Federal MCL |
California Standard |
Note |
| Chromium-6 |
No specific limit (total Cr: 100 ppb) |
10 ppb (reinstated 2024) |
California is the only state with a Cr-6 specific limit |
| 1,2,3-TCP |
No federal MCL |
5 ppt |
Industrial solvent; common in CA groundwater |
| Perchlorate |
0.056 mg/L (2024) |
6 ppb |
Rocket fuel component; thyroid disruptor |
| Lead |
Action Level: 15 ppb |
Action Level: 10 ppb (2025 target) |
CA aligning with updated Lead and Copper Rule |
| Arsenic |
10 ppb |
10 ppb |
Same; EWG guideline is 0.004 ppb |
The Consumer Confidence Report (CCR): What It Tells You and What It Doesn't
Every utility serving 25+ people must issue an annual CCR (also called the "Water Quality Report") by July 1. It must disclose:
- Source water type (surface, groundwater)
- All detected regulated contaminants and their levels vs. MCLs
- Any violations in the past year
- Potential health effects of any violation
What CCR Does NOT Disclose
Unregulated contaminants (no MCL = no required reporting)
Contaminants detected below the MCL (legal but potentially harmful)
Lead levels at the tap (utility tests at the treatment plant)
Comparison to health-protective thresholds vs. only legal ones
EWG Database Fills the Gap
Uses utility-submitted test data to compare against health guidelines
Includes unregulated contaminants utilities tested for voluntarily
Searchable by utility, zip code, city
Updated regularly as utilities submit new data
Module 03
Residential Water
Treatment
Estimated reading time: 6 minutes
Not all filtration is created equal. Matching the right technology to the specific contaminant profile is critical for effective residential water treatment.
Filtration Technologies
💧
Activated Carbon
Reduces chlorine, chloramines, VOCs, and bad tastes/odors. Ineffective against heavy metals (unless modified) or dissolved solids.
🔬
Reverse Osmosis (RO)
Forces water through a semi-permeable membrane. Highly effective for a broad spectrum including heavy metals, PFAS, and nitrates.
⚡
Ion Exchange
Swaps calcium and magnesium ions for sodium or potassium. Primary method for water softening. Does not remove chemical contaminants.
☀️
UV Purification
Neutralizes bacteria and viruses using ultraviolet light. Requires pre-filtration to ensure water clarity for maximum UV exposure.
Module 04
Field Application
Standards
Estimated reading time: 5 minutes
Professionalism and accuracy are paramount. This module covers compliance, ethical conduct, and proper attribution when discussing water quality with residents.
Proper Attribution and Conduct
When presenting data, always attribute it to the source (e.g., EWG Tap Water Database or the local utility's CCR). Never make medical claims or guarantee health outcomes.
- Do: Show residents their local water report from verifiable sources.
- Do: Explain the difference between legal limits and health guidelines.
- Don't: Use scare tactics or exaggerate risks.
- Don't: Claim a system removes 100% of all contaminants.