How to test your tap water properly

Your water utility's published results describe water leaving its treatment plants, averaged across sampling events. Your tap is at the end of distribution mains, a service line and household plumbing, any of which can add lead, copper or particulates that the utility's numbers do not capture.

For lead in particular, the utility's own compliance sampling is designed to characterise the system, not your house. Household lead almost always comes from the service line, solder or fixtures, so it is a property-specific question by nature.

• A standard panel from an accredited lab covers the common ground: metals including lead and copper, hardness, nitrate, chloride, pH and often bacteria. Roughly $100 to $200 by mail.
• A PFAS panel is separate and must be ordered specifically, typically $150 to $300. No standard panel includes PFAS.
• If you are on a well, add bacteria (total coliform and E. coli), nitrate and arsenic as a baseline, and radon in water if you are in a high-radon area.
• If your area has industrial history, ask the lab about a VOC panel, which covers solvents such as TCE and PCE.

Use a laboratory accredited for drinking water analysis under your state's programme or the national NELAP scheme. Accreditation is what makes a result usable in a conversation with a utility or a landlord.

Follow the kit's instructions exactly, because the two common tests want opposite things. A first-draw lead sample requires water that has sat in the pipes at least six hours untouched, since the point is to measure what leaches from your plumbing. A general chemistry or PFAS sample usually wants the tap run first to flush the line.

Do not sample from a tap with an aerator screen full of debris, do not use a filtered tap unless you are deliberately testing the filter's output, and do not rinse the bottle: PFAS bottles in particular are prepared and preserved, and rinsing invalidates them.

If you want to know whether your filter works, take two samples: one before, one after. That is the only way to tell.

Results arrive as a value, a unit and usually a reference limit. Compare against the federal maximum contaminant level where one exists: 15 ug/L action level for lead, 10 mg/L for nitrate, 10 ug/L for arsenic, 4 ng/L for PFOA and PFOS.

Watch the units, which differ by contaminant: metals in ug/L or mg/L, PFAS in ng/L. Mixing them up by a factor of a thousand is the most common misreading of a water report.

A 'non-detect' means below the laboratory's reporting limit, not zero. The reporting limit is on the report and is worth reading, because a non-detect at a high reporting limit says less than one at a low limit.