What is in Orange County's tap water, across all 28 districts

Every contaminant the county's districts publish

These are the ones enough districts report for a county figure to mean something. We state one only where at least 17 of 28 districts published a number, because a median over a handful of districts mostly describes which reports we could obtain rather than the county’s water.

“Over the line” means different things by contaminant, and the table says which on every row. For most it is a health-based concentration. For hexavalent chromium it is a laboratory detection, because California’s health goal for it sits below what any instrument can measure, so counting districts “above” it would flag every detection by arithmetic and mean “found” rather than “high”.

Lead and copper: measured at the tap, not in the supply

Lead and copper behave differently from everything else here: they are a property of your plumbing, not of the water a district delivers. Both enter between the water main and the tap, so a district measures them by sampling inside a set of higher-risk homes and reporting the 90th percentile. That number describes those homes, not the supply, which is why it sits here rather than in the table above.

It is also the best news in the county. 24 of 28 districts report no detectable lead at all. 4 report a number, and the highest of those is 6 ppb, against a federal action level of 10 ppb. Copper is present everywhere, as it is anywhere with copper pipe, at a county median of 0.17 ppm against a 1.3 ppm action level.

None of that describes your house. A district’s 90th percentile is drawn from a sample of homes chosen to be higher-risk than average, and your own plumbing, fixtures and how long water sits in them decide what comes out of your tap. It is the one thing on this page that only a test at your own tap can answer.

What too few districts report to say anything about

We hold readings for the rest of the panel too, from too few districts to state a county figure. They are listed because leaving them out would imply we looked at nothing else, and because the reason a cell is empty matters. An empty cell means one of three things: the district tested and found nothing, the district published no value, or we have a gap in our own reading.

A district that published no value has usually not skipped the test. 26 of these 28 districts buy treated water from a wholesaler, and for a bought supply the plant-level contaminants are typically sampled upstream under the wholesaler’s permit number and reported there instead. An empty cell is a question about where the measurement was filed, not evidence that the water was clean.

Uranium is held back. Twenty-six districts publish a uranium figure, but they publish it in picocuries per litre and the only uranium health line in our registry is a mass concentration in micrograms per litre. Converting between the two needs an isotopic assumption we would be inventing, so the readings are held rather than graded.

Hard water: real, expensive, and not a health problem

Orange County water is hard. Across the 24 districts that publish a hardness figure the median is 242 milligrams per litre as calcium carbonate, running from 66.1 to 392. Anything above about 180 is classed as “very hard”, so most of the county is well inside that band.

Hardness is dissolved calcium and magnesium. It is what leaves scale in a kettle, shortens the life of a water heater, spots glassware, and makes soap harder to rinse. Those are real costs and a softener genuinely fixes them. What hardness is not is a health risk: no health-based limit exists for it anywhere, and the evidence does not support treating it as a contaminant.

We say this plainly because hardness is the single most searched thing about tap water, and much of what is written about it is sold by someone with a softener to move. If your water spots the glasses and scales the kettle, that is hardness doing exactly what hardness does, and it tells you nothing about the contaminants above.

What this page cannot tell you

It is the county, not your district. Every figure here is a county figure, and the spread between districts inside Orange County is wide. Trihalomethanes alone run from 2 to 59 ppb, so a county median describes the region and does not predict any one supply. The address lookup is the tool for that, and every district publishes its own report in full through the state portal linked in the method below.

It is the district, not your house. Everything here stops where the water main meets your property. Lead and copper enter after that point, and so does anything your own plumbing, filters or water heater contribute.

It is the most recent report, not this morning. These reports cover 2023, 2024, 2025, because districts publish annually and not on the same schedule. A figure here is the most recent published one, not a live reading.

The PFAS limits are not yet in force. The federal PFOA and PFOS limits are approved but do not bind until April 2029. Where the table shows a district over one of those, it is over a rule that has not started, not in violation of one that has.