The list your report is not obliged to fill in
EPA sets 15 secondary standards covering taste, colour and odour.
It enforces none of them. And because they are not considered health threatening at those levels, systems “only need to test for them on a voluntary basis.”
That second sentence is the one worth keeping. A missing figure on your report may never have been measured, rather than having come back clean.
The symptom table
EPA’s own map from what you notice to what it might be.
| What you notice | Likely contaminant | Secondary standard |
|---|---|---|
| Metallic taste | Copper | 1.0 mg/L |
| Metallic taste, reddish or orange stains | Iron | 0.3 mg/L |
| Metallic taste | Zinc | 5 mg/L |
| Metallic taste, corroded fixtures | Corrosivity | Non-corrosive |
| Black or brown stains, bitter taste | Manganese | 0.05 mg/L |
| Salty taste | Chloride | 250 mg/L |
| Salty taste | Sulfate | 250 mg/L |
| Rotten-egg, musty or chemical smell | Odour | 3 TON |
| Visible tint | Colour | 15 colour units |
| Coloured water | Aluminium | 0.05 to 0.2 mg/L |
| Frothy, cloudy, bitter | Foaming agents | 0.5 mg/L |
| Bitter metallic taste, corrosion | pH below range | 6.5 to 8.5 |
| Slippery feel, soda taste, deposits | pH above range | 6.5 to 8.5 |
| Hardness, deposits, staining, salty taste | Total dissolved solids | 500 mg/L |
| Tooth discolouration | Fluoride | 2.0 mg/L |
| Skin discolouration | Silver | 0.1 mg/L |
Several symptoms have more than one candidate. Only a test separates them.
Three kinds of problem, and one that matters more
EPA sorts them into three groups.
Aesthetic — undesirable tastes or odours.
Cosmetic — effects which do not damage the body but are still undesirable.
Technical — damage to water equipment, or “reduced effectiveness of treatment for other contaminants.”
That last phrase is the one to notice. A technical-category problem can reduce how well treatment works on something that is regulated.
Corrosivity sits in this group, alongside iron, pH and total dissolved solids.
The one secondary standard with a duty attached
Fluoride, and only fluoride.
EPA requires a special notice for exceeding the fluoride secondary standard of 2.0 mg/L. A community system above 2.0 but below the enforceable 4.0 mg/L limit must notify customers “no later than 12 months” from learning of it, under 40 CFR 141.208.
That is a notice, not a violation. The system is not required to treat.
Twelve months is also the Tier 3 timeframe, so such a notice may arrive attached to your annual report rather than separately.
→ Fluoride: the numbers, and which one is a limit
Colour is the one that points somewhere regulated
Most of this list is comfort. Colour is the exception worth following up.
EPA states colour “may be indicative of dissolved organic material, inadequate treatment, high disinfectant demand, and the potential for the production of excess amounts of disinfectant by-products.”
Dissolved organic material is the precursor that becomes trihalomethanes and haloacetic acids, which do have enforceable limits.
EPA also notes complaints begin anywhere from five to 30 colour units, and that most people object above 15.
So coloured water is a reason to read the byproduct lines on your report, not a reason to buy anything yet.
→ Disinfection byproducts, and what the numbers mean
A standard that exists because of home filters
A detail worth knowing on a site about filters.
Silver has a secondary standard of 0.1 mg/L for skin discolouration, called argyria. EPA states it “does not impair body function” and “has never been found to be caused by drinking water in the United States.”
The standard exists anyway, EPA says, “because silver is used as an antibacterial agent in many home water treatment devices.”
One of the 15 is there because of the treatment industry rather than the water.
What actually fixes these
EPA frames the answers at plant scale, not household scale.
Corrosion control is, in EPA’s words, perhaps the single most cost-effective method for iron, copper and zinc. It is also the utility’s job, not yours.
Granular activated carbon removes most of what causes odours, colour and foaming. That is the one with a household equivalent.
Aeration handles odours, iron and manganese. Coagulation and filtration handle iron, manganese and zinc.
Reverse osmosis, distillation and electrodialysis address chloride and total dissolved solids, and EPA calls them expensive.
→ Which claims exist in which product form
The decision framework
1. Name the symptom precisely
Metallic, salty, rotten-egg and musty point at different rows. “Bad taste” does not narrow anything.
2. Check whether the figure is even on your report
If it is absent, nobody was required to measure it. Ask the utility what it monitors voluntarily.
→ How to read your water quality report
3. Separate nuisance from signal
Salty, metallic and hard are comfort problems. Coloured water and corrosivity are worth following into the regulated lines.
4. Treat corrosion symptoms as information about your plumbing
Copper and blue-green staining usually come from your own pipes, downstream of every sample the utility takes.
→ Copper, and the stain that warns you about lead
5. If you do buy something, buy against a claim
Carbon is certified for chlorine taste and odour in thousands of models. Most other symptoms here have no matching certified claim at all.
→ Which claims exist at all, and how populated each is
The decision path
| What you notice | What it probably is | What follows |
|---|---|---|
| Chlorine smell | Disinfectant residual, required by law | Carbon; thousands of certified models |
| Rotten-egg smell | Hydrogen sulfide; no standard exists | Nuisance, but test if on a well |
| Blue-green stains | Copper from your plumbing | Test copper and lead together |
| Reddish or orange stains | Iron above 0.3 mg/L | Nuisance; utility may not monitor it |
| Black or brown stains | Manganese above 0.05 mg/L | Ask the utility; infants are a separate case |
| Salty taste | Chloride or sulfate at 250 mg/L | Nuisance; RO if it bothers you |
| Cloudy white, clears upward | Dissolved air | Nothing at all |
| Visible tint or colour | Organic material or metals | Read the byproduct lines |
| Fluoride between 2.0 and 4.0 | Above secondary, below the limit | You should receive a notice within 12 months |
| Tastes fine | Tells you nothing about lead or PFAS | Read the report anyway |
Choose to act if
- The symptom is coloured water, which can indicate the organic precursors to regulated disinfection byproducts.
- You see blue-green or black staining, which points at copper or manganese and therefore at a test worth paying for.
- The nuisance genuinely bothers you enough to spend on comfort. That is a legitimate reason, just not a health one.
Choose to investigate before buying if
- The figure is not on your report. Voluntary monitoring means a blank is not a result.
- Several contaminants share your symptom, which is true for metallic taste and for salty taste.
Choose to do nothing if
- The water clears from the bottom up in a glass. That is dissolved air.
- The taste is chlorine on a compliant supply. That residual is a legal requirement, not a fault.
→ Chlorine and chloramine on city water
Mistakes that cost the most money
Reading a blank line as a clean result. Secondary monitoring is voluntary. Nobody had to measure it.
Treating good taste as a safety verdict. Lead cannot be seen, tasted or smelled. Neither can PFAS or nitrate.
Buying a system for a nuisance without checking for a certified claim. Most of these symptoms have no matching NSF claim, so nothing can be verified.
Fixing staining without testing. Blue-green points at copper, and copper comes from the same corrosion that mobilises lead.
Assuming a smell means danger. Hydrogen sulfide has no standard at all, because it becomes undrinkable long before it becomes harmful.
Ignoring coloured water. It is the one symptom on this list that can indicate something with an enforceable limit behind it.
Three situations, and what changes
A new flat, water tastes strongly of chlorine. That is a disinfectant residual your utility is required to maintain, not a defect. A certified carbon filter addresses it in thousands of listed models, and this is the one symptom on the page with a deep certified field behind it.
Blue-green staining around the plughole. Copper, above or near its 1.0 mg/L secondary standard, and almost certainly from your own plumbing. The useful response is a copper and lead test rather than a filter purchase, because the corrosion that carries one carries the other.
Water with a faint yellow tint after heavy rain. Colour, likely from dissolved organic material in the source. It is aesthetic on its own, but it is the precursor to disinfection byproducts, so the next place to look is the TTHM and HAA5 lines of the annual report.
The objections worth answering
“If EPA set a number, someone must be checking it.” Not necessarily. EPA does not enforce secondary standards and systems test for them voluntarily. The fluoride notice is the single federal duty attached to any of them.
“Bad taste means bad water.” It means an aesthetic threshold has been crossed. EPA notes odour-free water is not necessarily safe to drink, and the reverse holds too.
“These are just cosmetic, so ignore them.” Two are not. Colour points at byproduct precursors, and the technical category is defined partly by reduced effectiveness of treatment for other contaminants.
“A whole-house filter will handle all of it.” Very little is certified at whole-house scale. Chlorine and taste-and-odour claims are the exception.
“My water is cloudy, so it needs filtering.” Cloudiness that clears from the bottom upward is dissolved air. Cloudiness that does not clear is worth measuring against the turbidity line instead.
→ Turbidity: the line that is really a pathogen check
Who this is for
Households on a public supply trying to work out what a taste, smell or stain means, and whether it warrants spending anything.
It is also for anyone who has been told a sensory complaint proves their water is unsafe, or that clean-tasting water proves it is fine. Neither follows.
Private wells share the symptoms but not the monitoring.
→ Well water: the six-parameter test panel
What to settle first
Is the figure for my symptom actually on the report, and is it one of the two that point somewhere regulated?
A blank is not a pass. And colour and corrosivity are the rows worth following further than the rest.
→ How to read your water quality report → What a TDS meter actually measures → Manganese: three numbers, none enforceable → City water treatment, and the three gaps a utility cannot close → Testing city water: what your utility already measured → Earthy or musty taste, and why it is not the toxin → Water age: one variable behind several of these symptoms