Drinking Water Quality Standards Reference
Why this matters
Water treatment recommendations are grounded in regulatory standards. The EPA, the Safe Drinking Water Act (SDWA), and various state regulations establish what's considered safe vs. concerning vs. urgent. Customers ask "is my water safe?" - the answer depends on what's being measured and how it compares to established standards. A technician without working knowledge of the relevant standards can't answer the question authoritatively. This reference covers the standards a residential water treatment technician should know.
The framework
US drinking water standards are organized into:
Primary standards (enforceable, federal):
- Maximum Contaminant Levels (MCLs)
- Set to protect public health from acute / chronic effects
- Required compliance for public water systems
- EPA-published list at 40 CFR 141.62, 141.66, 141.80, and similar
Secondary standards (advisory, not federally enforceable):
- Set for aesthetic concerns (taste, odor, color, staining)
- States may or may not enforce
- EPA-published list at 40 CFR 143
Maximum Contaminant Level Goals (MCLGs):
- The level at which no health effects are expected
- Often zero for cancer-causing contaminants (no safe level)
- Not enforceable but informative
The customer's water is "safe" by federal standard if it meets all primary MCLs. Individual customers may want tighter standards for their specific concerns.
Major primary contaminants
| Contaminant | EPA MCL | Health concern |
|---|---|---|
| Lead | 15 µg/L (action level) | Neurological, especially children |
| Copper | 1.3 mg/L (action level) | Acute GI distress at high levels |
| Arsenic | 10 µg/L | Cancer, skin, cardiovascular |
| Nitrate (as N) | 10 mg/L | Methemoglobinemia in infants |
| Nitrite (as N) | 1 mg/L | Same as nitrate, more acute |
| Fluoride | 4 mg/L | Skeletal fluorosis; teeth |
| Trichloroethylene (TCE) | 5 µg/L | Cancer, kidney |
| Perchloroethylene (PCE) | 5 µg/L | Cancer, kidney |
| Benzene | 5 µg/L | Cancer |
| Trihalomethanes (TTHM) | 80 µg/L | Cancer, reproductive |
| Haloacetic Acids (HAA5) | 60 µg/L | Cancer |
| Total Coliforms | 0 CFU per 100 mL | Indicator of fecal contamination |
| E. coli | 0 CFU per 100 mL | Pathogen |
| Cryptosporidium | TT (treatment technique) | Acute GI |
| Giardia | TT (treatment technique) | Acute GI |
Major secondary contaminants
| Contaminant | EPA Secondary Standard | Concern |
|---|---|---|
| Aluminum | 0.05-0.2 mg/L | Cosmetic / aesthetic |
| Chloride | 250 mg/L | Taste |
| Color | 15 color units | Appearance |
| Copper | 1.0 mg/L | Staining (this is secondary; lead/copper action level is separate) |
| Corrosivity | Non-corrosive | Pipe damage |
| Fluoride | 2.0 mg/L | Cosmetic (tooth staining) |
| Foaming agents | 0.5 mg/L | Aesthetic |
| Iron | 0.3 mg/L | Staining, taste |
| Manganese | 0.05 mg/L | Staining, taste |
| Odor | 3 (TON) | Aesthetic |
| pH | 6.5-8.5 | Plumbing damage, taste |
| Silver | 0.10 mg/L | Aesthetic |
| Sulfate | 250 mg/L | Taste, laxative effect at higher levels |
| Total Dissolved Solids (TDS) | 500 mg/L | Taste |
| Zinc | 5 mg/L | Aesthetic |
What "exceeds the standard" means
For primary contaminants:
- Public water systems must comply
- If a customer's water exceeds the standard, the utility must address it
- Private wells are NOT regulated under SDWA; the customer is the responsible party
- Lab results showing exceedance are typically reported to the utility for action
For secondary contaminants:
- Aesthetic / quality of life
- Customers may choose to treat for aesthetic reasons
- Not enforced federally; some states require treatment
Private wells
Private wells (well that serves only one household or under 25 people total):
- NOT regulated under SDWA
- Customer is responsible for water quality
- State public health departments often offer testing
- Many states require pre-purchase testing for real estate transactions
- Standard practice: annual testing for coliform bacteria, every 3-5 years for full panel
A well-owning customer's water "safety" is their responsibility; the water treatment company helps them assess and address concerns.
Lab tests for residential customers
Standard residential water test packages:
Basic test (minimum recommended for any well):
- Coliform bacteria (E. coli)
- Nitrate, nitrite
- pH
Standard test (recommended for new wells, annual testing):
- Above plus:
- Hardness
- Iron, manganese
- Lead, copper
- Total dissolved solids
- Sulfate, chloride
Comprehensive test (recommended every 3-5 years OR when concerns arise):
- Above plus:
- VOCs (volatile organic compounds)
- Pesticides
- Heavy metals (arsenic, cadmium, chromium, mercury)
- Radon
- Fluoride
Costs vary by state; Cooperative Extension labs are typically lowest cost.
What customers commonly want tested
Customer-driven tests:
- "Is my water safe?" → Standard test
- "My water tastes bad" → Hardness, iron, manganese, TDS, chloride
- "My fixtures are stained" → Iron, manganese, hardness, copper
- "My pipes are corroding" → pH, hardness, alkalinity, copper, lead
- "My family member has health concerns" → Comprehensive test + lead specifically
- "I want bottled-water quality" → TDS, taste-related contaminants
- "I just bought this property" → Comprehensive test as baseline
Interpretation of test results
Standard report format:
| Parameter | Value | MCL / Standard | Status |
|---|---|---|---|
| pH | 6.4 | 6.5-8.5 (secondary) | Below acceptable; treatment recommended |
| Hardness | 18 GPG (308 mg/L CaCO3) | None federal | Hard water; softening recommended |
| Iron | 0.45 mg/L | 0.3 mg/L (secondary) | Above standard; treatment recommended |
| Lead | 12 µg/L | 15 µg/L (action level) | Below action level but elevated; investigate |
| Coliform | Absent | 0 CFU / 100mL | Acceptable |
| Nitrate | 4 mg/L | 10 mg/L | Acceptable |
Communicating with the customer:
- Explain each result in plain language
- Identify any that exceed standards
- Discuss treatment options for each
- Note any that are within standards but might benefit treatment (aesthetic preference)
Treatment recommendations linked to results
| Result | Standard treatment recommendation |
|---|---|
| pH < 6.5 | pH neutralizer (calcite) |
| Hardness > 7 GPG | Water softener |
| Iron > 0.3 mg/L | Iron treatment system |
| Lead > 5 µg/L | POU RO at drinking water |
| Coliform positive | Investigate well; UV + chlorination |
| Nitrate > 5 mg/L | Investigate source; POU RO for drinking water |
| VOCs detected | Carbon filtration + investigation |
| Chloramine in municipal | Catalytic carbon |
Drinking water vs. household water
References
- Safe Drinking Water Act (SDWA), 1974 + amendments
- 40 CFR 141 (National Primary Drinking Water Regulations)
- 40 CFR 143 (National Secondary Drinking Water Regulations)
- EPA Drinking Water Contaminants List
- WHO (World Health Organization) Drinking Water Guidelines
- NSF/ANSI Standards
- State Cooperative Extension water-testing services
- Manuall internal: Lead and Copper Testing, Well Water Testing, Diagnose Hard Water