What Is the Surface Water Treatment Rule?

By SubcontractorHub Editorial Team·Published October 2026

Dealers who sell treatment sometimes meet a customer who has a city-water notice, not a private-well jug. The surface water treatment rule is a public-system rule. It is not a kitchen-tap MCL for a single house, and it is not a filter model. SubcontractorHub is software for the customer record. This page is the public note. It is not a plant design.

A public water system, as a category, is already explained on what a public water system is. Turbidity as a measurement, including why a cloudy sample is not the same sentence as this rule, is turbidity in well water. This article stays on the surface water treatment rule.

Who the Surface Water Treatment Rule Names

EPA's national primary page, footnote 3, fetched the day this page was written, says the surface water treatment rules require systems using surface water or ground water under the direct influence of surface water to disinfect their water, and to filter their water or meet criteria for avoiding filtration. The contaminants named in that control list include Giardia lamblia, viruses, Legionella, Cryptosporidium, turbidity, and heterotrophic plate count.

Giardia lamblia is listed at 99.9 percent removal or inactivation. Viruses are listed at 99.99 percent removal or inactivation. Legionella has no limit on that note. The sentence says EPA believes that if Giardia and viruses are removed or inactivated according to the treatment techniques in the Surface Water Treatment Rule, Legionella will also be controlled. That belief is not a separate number, and this page does not invent one.

The plain-English guide fetched the same day says the 1989 rule requires a Subpart H system to reduce the source-water concentration of Giardia lamblia and viruses by at least 99.9 percent (3-log) and 99.99 percent (4-log). It also says a detectable disinfectant residual must be maintained throughout the distribution system. It says the 1989 rule does not specifically control for Cryptosporidium. The national footnote's Cryptosporidium bullet, for unfiltered systems, is about including Cryptosporidium in existing watershed control provisions. Those are different sentences. Do not paste the Giardia percent onto Cryptosporidium.

What the Surface Water Treatment Rule Note Holds

The table above is the note. It is not a plant specification. A dealer who is looking at a private well is on a different rule set. A sanitary survey of a public system is a review of that system, explained on what a sanitary survey is. It is not this filtration percent.

Turbidity Lines, Without a Well-Water Guess

For systems that use conventional or direct filtration, the footnote says turbidity must not go higher than 1 nephelometric turbidity unit at any time, and samples must be less than or equal to 0.3 NTU in at least 95 percent of the samples in any month. Systems that use filtration other than conventional or direct filtration must follow state limits, which must include turbidity at no time exceeding 5 NTU. Heterotrophic plate count on the same note is no more than 500 bacterial colonies per milliliter.

A dealer reading a city notice should copy the system type and the number the notice actually prints. A 0.3 NTU line from this footnote is not a well-water MCL, and a 1 NTU ceiling is not a reason to tell a homeowner the jug failed. If the paper is a consumer confidence report, read that report on its own page. This rule is the plant duty.

Those lines measure filtration performance for the systems the footnote names. They are not a pass line for a kitchen tap on a private well, and they are not a reason to quote a cartridge as if it had met 0.3 NTU. If the lab sheet is a private well, say so. The well-water turbidity page is the place for that sample. This page does not move the 0.3 NTU sentence onto it.

What Should the Surface Water Treatment Rule Note Say?

Five lines keep a later visit from treating a city notice as a private-well MCL, or from copying Giardia's percent onto Cryptosporidium.

1. Whether the water is a public system on surface water or ground water under the direct influence of surface water.
2. The duty the footnote names: disinfect, and filter or meet criteria for avoiding filtration.
3. Giardia at 99.9 percent removal or inactivation, and viruses at 99.99 percent, named separately.
4. That the 1989 plain-English guide says Cryptosporidium is not specifically controlled by that rule.
5. What you did not claim: no cartridge percent, no installed price, and no statement that a single-home well is a Subpart H system.

Later Rules the Guide Names, and What They Do Not Add Here

The plain-English guide says the Interim Enhanced Surface Water Treatment Rule requires improved filtration performance by lowering the turbidity standard at systems that serve 10,000 or more people. It says the Long Term 1 rule extends that requirement to systems serving fewer than 10,000 people. It says the Long Term 2 rule requires additional treatment for Cryptosporidium at surface water or GWUDI systems with significant levels of Cryptosporidium in their source waters. It says the Filter Backwash Recycling Rule is meant to reduce pathogen concentrations by managing backwash water and waste streams.

The national footnote matches the population split in shorter form. Long Term 1 applies to surface water systems or groundwater under the direct influence serving fewer than 10,000 people. Long Term 2 applies to all such systems and targets additional Cryptosporidium treatment for higher-risk systems, plus provisions on uncovered finished-water storage and on keeping microbial protection while systems reduce disinfection byproducts. Filter backwash recycling requires systems that recycle to return specific recycle flows through all processes of the existing conventional or direct filtration system, or at an alternate location approved by the state.

None of those sentences is a product. Disinfection byproducts that can form when a system disinfects are a different cluster, including disinfection byproducts in drinking water. A private-well sample is still the well water testing guide. The software that holds the customer file is water treatment contractor software. This article does not size a filter and does not tell a household the water is safe to drink.

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