Cyanide in Well Water: The Public 0.2 mg/L Line

By SubcontractorHub Editorial Team·Published October 2026

A lab sheet can put fertilizer in more than one sentence. The digit next to free cyanide is not the digit next to nitrate measured as nitrogen. Dealers who sell treatment still have to say which public line they are reading. SubcontractorHub is software for the customer record. This page is the row. It is not a treatment design.

The Public 0.2 mg/L Line for Cyanide in Well Water

The national primary drinking water regulations are legally enforceable primary standards and treatment techniques that apply to public water systems. In the inorganic block, cyanide as free cyanide shows an MCLG of 0.2 and an MCL of 0.2. The potential health effects cell says nerve damage or thyroid problems. The source cell says discharge from steel and metal factories, and discharge from plastic and fertilizer factories.

Footnote 2 says units are in milligrams per liter unless otherwise noted, and that milligrams per liter are equivalent to parts per million. 0.2 mg/L is therefore 0.2 ppm on that note. It is not a second standard hiding under a different name. Moving the same digits to micrograms per liter uses the 1,000-to-1 scale on milligrams and micrograms. 0.2 mg/L is 200 µg/L on that scale. Write both labels if the lab used the smaller unit, so a later reader does not think 200 is a new limit.

An MCLG is a goal. An MCL is the enforceable public number. On this row the two cells print the same digit. That match is not true of every neighbor, and it is not a reason to drop the words "as free cyanide." The definitions of those two words are on MCL and MCLG. A goal is not a fine, and a matching pair is still one line with a specific chemical name.

The 0.2 mg/L Figure in the Inorganic Table

Section 141.62, as printed on the Cornell eCFR page fetched the same day, lists maximum contaminant levels for inorganic contaminants. Cyanide as free cyanide is item (13), at 0.2 mg/L. Fluoride, item (1) on that table, is 4.0 mg/L, and paragraph (b) says that fluoride level only applies to community water systems. The fluoride row has its own page, fluoride in well water. Do not copy the community-only sentence onto item (13). Item (13) sits in the (11) through (16) group.

Paragraph (b) says the levels in items (11) through (16), which include item (13), apply to community and non-transient, non-community water systems. Nitrate, nitrite, and total nitrate and nitrite are items (7), (8), and (9). Those three also apply to transient non-community systems. A private well is not named in any of those sentences. A dealer who copies the 0.2 mg/L line onto a kitchen-tap jug still has to say the jug is not the public-system rule. The difference between a city system and a private well is what is a public water system.

Cyanide in Well Water Is Not the 10 mg/L Nitrate Row

Nitrate measured as nitrogen prints an MCLG of 10 mg/L and an MCL of 10 mg/L on the same national table. The health cell says infants below the age of six months who drink water containing nitrate in excess of the MCL could become seriously ill and, if untreated, may die, and that symptoms include shortness of breath and blue-baby syndrome. The source cell says runoff from fertilizer use, leaking from septic tanks and sewage, and erosion of natural deposits. That is a different contaminant, a different digit, and a different source sentence. The nitrate page is nitrates in well water.

The source sentence you are allowed to repeat from this fetch is discharge from steel and metal factories, and discharge from plastic and fertilizer factories. Fertilizer factories are not the same words as runoff from fertilizer use. If the lab header says free cyanide, that is the source cell. Adding 0.2 and 10 does not create a limit the rule printed.

What the Note Holds, and What It Does Not

The table above is the note. It is not a quote, and it is not a removal design. A customer who wants a price still needs a test, a model, and a scope. Those live on the job. This page only stops the wrong digit from landing in the scope, and it keeps the words "as free cyanide" attached to 0.2 mg/L.

What the BAT Marks Do Not Promise

The BAT table on the same Cornell page marks cyanide as 5, 7, and 13. The key says 5 is ion exchange. The key says 7 is reverse osmosis. The key says 13 is alkaline chlorination at a pH of 8.5 or higher. Those marks identify a technology the rule names for compliance with the MCL. They do not say what percent a cartridge in a basement will remove.

A city plant and a point-of-use tank are not the same machine. If you sell reverse osmosis, say you sell reverse osmosis. Do not say the number 7 is a guarantee on this well. The pH figure in mark 13 is part of the technology name on the key. It is not a drinking-water pH limit this page is setting, and it is not a removal percentage. No removal percentage was fetched for this row, so none is printed here.

What Should the Cyanide in Well Water Note Say?

Five lines keep the next visit from borrowing nitrate. Name free cyanide the way the lab printed it, show the unit before anyone compares it with 0.2, and say whether the jug is a private well. If a line does not apply, mark it skipped. A blank line looks the same as a step you forgot, and a skipped line is still a line someone can read later.

1. The name as the lab printed it, including whether it says free cyanide, not a panel total.
2. The result and the unit. If the unit is µg/L, show the mg/L equivalent on the 1,000 scale before anyone compares it with 0.2.
3. The public pair you compared it with: MCLG 0.2 mg/L and MCL 0.2 mg/L, named as the national free-cyanide row.
4. Whether the sample is a private well or a public system. Paragraph (b) names community and non-transient, non-community systems for item (13).
5. What you did not claim: no removal percent, no installed price, and no statement that 0.2 mg/L is nitrate's 10 mg/L.

Where the Row Sits on the Job

The lab sheet belongs with the customer, the address, and the date of the sample. A price for equipment is a later page, after someone has read this row and the rows next to it. Mixing the 0.2 mg/L line into a nitrate quote because both source cells mention fertilizer skips the chemical name.

How a dealer reads a full panel, including which tests were actually run, is 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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