Secondary Water Standards – What’s In My Water?

There are many substances that show up in our tap water that are regulated by the government, but also many that are not. Laws cover substances that have mandatory regulations (lead, copper, etc.) but other material that we don’t want in our water is not deemed as unsafe and thus isn’t as tightly regulated (sometimes not regulated at all!) or as closely watched. These generally fall under the list of what’s known as “Nuisance Chemicals” and are covered by “Secondary Drinking Water Standards” or the National Secondary Drinking Water Regulations (NSDWRs). These are recommended standards from the EPA, not enforceable or mandatory limits. Water regulations are also outlined in Title 40 Section 141 of the Code of Federal Regulations.

This list, though unenforced, is known as the secondary maximum contaminant levels (SMCLs) and it’s something to keep an eye on if you have access to your water data or ever have your water tested and need a reference point.

Why do these levels matter? Because it’s very possible for your water to be safe and within the confines of the EPA’s regulations, but still taste, smell, or look weird. The water could also be damaging home plumbing equipment or going through filters very quickly.

What are some common materials that affect the taste and smell of water? The EPA SMCL list says you should track:

Chloride, Copper, Foaming Agents, Iron, Manganese pH, Sulfate, Threshold Odor Number (TON), Total Dissolved Solids, Zinc

The EPA lists foaming of water as a completely different issue unrelated to any of these. If your water is foaming you want to look out for “Foaming Agents” (um, thanks EPA). We did some further digging and basically you are searching for surfactants. Most of these are odorless, but will impart the water with a “oily, fishy, and perfume-like” taste.

Water can also affect your body in a “cosmetic” sense. Skin discoloration can be caused by silver in your water (though this has never happened in the US) and excessive amounts of fluoride in water can cause teeth to change color (browning) or even be harmed through poor enamel structure and pitting of the teeth in extreme cases.

The final category of SMCLs creates what the EPA calls “technical effects” or those affecting your home, mostly through corrosion or discoloration. The list includes the levels of:

Chloride, Copper, Corrosivity, Iron, Manganese, pH, Total Dissolved Solids, Zinc

Most of which will cause corrosion and blue-green discoloration on fixtures.

Lastly, excess amounts of the following:

Iron, pH, Total Dissolved Solids, Aluminum

Will cause scaling (mineral deposits) on shower heads, inside coffee makers, and so on. This will make your water boiler, water heater, espresso machine, and other items that come in direct contact with the water less effective.

EPA Table of Secondary Standards

The table is measured in milligrams per liter of water and uses the abbreviation “MCL” for “maximum contaminant level.”



Effect(s) when above MCL

Aluminum 0.05 to 0.2 mg/L* colored water
Chloride 250 mg/L salty taste
Color 15 color units visible tint
Copper 1.0 mg/L metallic taste; blue-green staining
Corrosivity Non-corrosive metallic taste; corroded pipes/ fixtures staining
Fluoride 2.0 mg/L tooth discoloration
Foaming agents 0.5 mg/L frothy, cloudy; bitter taste; odor
Iron 0.3 mg/L rusty color; sediment; metallic taste; reddish or orange staining
Manganese 0.05 mg/L black to brown color; black staining; bitter metallic taste
Odor 3 TON (threshold odor number) “rotten-egg”, musty or chemical smell
pH 6.5 – 8.5 low pH: bitter metallic taste; corrosion
high pH: slippery feel; soda taste; deposits
Silver 0.1 mg/L skin discoloration; graying of the white part of the eye
Sulfate 250 mg/L salty taste
Total Dissolved Solids (TDS) 500 mg/L hardness; deposits; colored water; staining; salty taste
Zinc 5 mg/L metallic taste