Primary and Secondary Drinking Water Standards: Two Tables

By SubcontractorHub Editorial Team·Published October 2026

Dealers mix these up because a lab PDF can print both kinds of numbers in one grid. The two columns inside the primary table, a goal and a standard, are MCL and MCLG. This page is the other split: which table the number came from. SubcontractorHub is an all-in-one sales and project management platform for solar, roofing, and HVAC contractors. Water-treatment dealers use the same job record to keep the table name next to the result.

What Primary and Secondary Drinking Water Standards Each Do

The national primary drinking water regulations are legally enforceable primary standards and treatment techniques that apply to public water systems. They limit contaminants to protect public health. An MCL is the highest level of a contaminant that is allowed in drinking water. MCLs are enforceable standards. An MCLG is the level below which there is no known or expected risk to health. MCLGs allow a margin of safety and are non-enforceable public health goals.

The secondary drinking water standards are a second set. EPA established them as non-mandatory water quality standards for 15 contaminants. EPA does not enforce these secondary maximum contaminant levels. They assist public water systems with aesthetic considerations such as taste, color, and odor. The page says these contaminants are not considered to present a risk to human health at the SMCL.

That last sentence is about the secondary level, not a promise that every primary contaminant is harmless below its MCL. Keep the tables apart. A salty taste can be a secondary chloride line. A primary metal line is a different kind of number, even when both appear on one PDF.

Secondary Figures Dealers Already See

These rows are copied from the secondary table fetched for this page. Each one is a public guideline. None of them is rewritten here as a private-well limit.

The full secondary table also lists color at 15 color units, copper at 1.0 mg/L, corrosivity as non-corrosive, foaming agents at 0.5 mg/L, odor at 3 TON, and silver at 0.1 mg/L. Aluminum's range is printed as 0.05 to 0.2 mg/L, not a single digit. Do not collapse that range into one cutoff.

Where Those Rows Already Live on This Site

Chloride at 250 mg/L is chloride in well water. Sulfate at 250 mg/L is sulfate in well water. Total dissolved solids at 500 mg/L is TDS in well water. The pH range is well water pH. Manganese at 0.05 mg/L is manganese in well water. Iron at 0.3 mg/L is the secondary rusty-water line; the filter conversation is iron filter for well water.

Fluoride is the row that sits on both tables. Primary 4.0 mg/L and secondary 2.0 mg/L are written out in fluoride in well water. The secondary page also says community systems that exceed 2.0 mg/L but not the 4.0 mg/L MCL must give public notice within 12 months. That notice is not an SMCL for the other 14 contaminants.

What to Mark Before You Call a Number a Violation

1. Which table the figure came from: primary or secondary.
2. Whether the primary figure is an MCL, an MCLG, or a treatment technique.
3. The unit. Note 2 on the primary page says milligrams per liter unless otherwise noted, equivalent to parts per million.
4. That both tables, as fetched, apply to public water systems.
5. The sample point, so a later visit does not compare a new bottle with an old one.
6. No removal percentage copied from a general treatment paragraph.

Effects the Secondary Page Groups

The secondary page groups problems into aesthetic effects, cosmetic effects, and technical effects. Aesthetic effects are undesirable tastes or odors. The page ties chloride, copper, foaming agents, iron, manganese, pH, sulfate, odor, total dissolved solids, and zinc to taste or odor, and it ties aluminum, color, copper, iron, manganese, and total dissolved solids to color.

Cosmetic effects on that page are skin discoloration from silver, and tooth discoloration from fluoride. Technical effects are corrosion and staining, and scale and sediment. Corrosion control is described as a public-system practice that can reduce metals leaching from pipes. The page says corrosion control is not used to remove metals from contaminated source waters. That sentence matters. A pipe problem and a source problem are not the same job.

The page also says federal regulations do not require public systems to monitor and treat for secondary contaminants, though state agencies and systems often do. It names conventional treatment, aeration, granular activated carbon, and, for chloride and dissolved solids, distillation, reverse osmosis, and electrodialysis, and it says those last three can be expensive and may be impractical for smaller systems. Those sentences are about public supplies. This page does not turn them into a household removal percent.

A Private Well Still Needs the Table Name

The testing sequence for a household well is the well water testing guide. Why a single-home well sits outside the public program is private well water regulations. Primary and secondary drinking water standards still belong on the ticket as labels, because the lab often prints them. The label is “public MCL” or “public SMCL,” not “this house failed.”

A water treatment dealer who writes the table name next to the number will not sell a health treatment for a taste guideline, or shrug off a primary line because a neighbor called the water fine. The record is the distinction. It is not a medical opinion, and it is not a device size.

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