How to Read Your Water Quality Report in Durham, NC

Triangle Waterworks · informational guide

Direct answer: Durham's annual water quality report names Lake Michie and Little River Reservoir as sources, lists TTHM, HAA5, PFOA, and PFOS against legal limits, and confirms atrazine and simazine were not detected. Read closely, it also reveals two gaps: no hardness figure anywhere, and every number is system-wide, not your tap. A free water analysis and an all-in-one softening-and-carbon system answer what the report can't.

Where Does Durham's Water Quality Report Come From?

Every community water system publishes an annual report summarizing what it delivered the previous year, and Durham's is no different. It names two surface-water sources, Lake Michie and the Little River Reservoir, treated at two separate facilities: the Williams and the Brown plants.

The report also discloses that Durham purchased water from the Town of Cary during the reporting year. That one line matters — it means "Durham's water," even read report line by line, is not exclusively Durham's own reservoirs.

You can read the full document yourself on the city's water quality page, linked in the Sources section below.

What Do MCL, LRAA, and RAA Mean on a Durham Report?

Two abbreviations do the work that a simple "average" doesn't capture. A Locational Running Annual Average (LRAA) is the average of four straight quarters of samples taken at one specific monitoring location — it tracks a single spot over a full year, not the whole system at once.

A Running Annual Average (RAA) is the same idea calculated across the entire distribution system instead of one location. The Maximum Contaminant Level (MCL) is the enforceable ceiling either figure gets measured against.

Both exist because a single system-wide average can hide a bad month at one sampling point. Reporting the highest LRAA, as Durham's report does for its disinfection byproducts, is the more conservative number — it reflects the worst-tested location, not a blend that smooths a spike away.

What Do ppb and ppt Mean, and Why Does Durham's Report Use Both?

Durham's report measures contaminants at very different scales, so it needs two units. Parts per billion (ppb) covers the disinfection byproducts, TTHM and HAA5. Parts per trillion (ppt) — a thousand times smaller than ppb — covers PFOA and PFOS, the "forever chemicals" now tracked at that scale nationwide. Mixing the two up when comparing a figure to its limit is the single most common way to misread any CCR.

What Does Durham's Report Show for Disinfection Byproducts?

This is where the numbers get real. Durham's highest reported TTHM (total trihalomethanes) LRAA is 56 ppb, against a legal MCL of 80 ppb. Its highest HAA5 (haloacetic acids) LRAA is 49 ppb, against an MCL of 60 ppb. Both are legally compliant, with no violations — and both are the highest verified disinfection-byproduct figures anywhere in our own service-area research.

EPA's National Primary Drinking Water Regulations table lists TTHM's potential health effect from long-term exposure above the MCL as "Liver, kidney or central nervous system problems; increased risk of cancer," and HAA5's as "Increased risk of cancer." Durham's water is compliant, and that's a real, verified fact — it shouldn't be read as a warning that anything is about to change.

But "compliant" describes a ceiling EPA set at the outer edge of its own acceptable risk, not a promise that nothing below it is worth addressing. TTHM and HAA5 are the exact compounds EPA had in mind when it drew that line, and an activated carbon stage removes them at your own tap rather than leaning on a legal limit to do the work.

What About PFAS and Pesticides in Durham's Water?

Durham's report shows PFOA at up to 5.7 ppt and PFOS at up to 7.2 ppt, both monitored with no violations. It also includes something a lot of CCRs skip: an explicit table naming atrazine and simazine, two common agricultural herbicides, sampled quarterly through 2025.

Both came back non-detect — under 0.1 ppb, against limits of 3 ppb and 4 ppb respectively. That's a genuinely clean result, and naming the compounds instead of leaving the line off entirely is a mark of a thorough report.

The report also states a chlorine residual running annual average of 0.63 ppm, with chloramines at 1.5 ppm — both maintained within legal limits all the way through the distribution system.

Here's what Durham's report shows at a glance, line by line:

Why Doesn't Durham's Report List a Hardness Number?

Because it simply doesn't — read cover to cover, Durham's report never states a hardness figure at all. That's not an oversight. Hardness isn't a federally regulated contaminant, so no CCR is required to report it, and Durham's doesn't. For a homeowner who opened the report specifically to find out whether the water is "hard," that's a real dead end, not a rounding error.

Our own testing across the service area, Durham included, measures 1.6 to 3.7 grains per gallon (gpg), depending on the address. On the Water Quality Association scale the Hach Total Hardness Test Kit (Model 5-B) uses, that range runs slightly hard to moderately hard. That's a field measurement, not a Durham-published figure — which is exactly why the report can't hand you your own number.

Why Does Durham's Report Show a System Number Instead of My Tap?

Because that's structurally what a CCR is built to report. Every figure in Durham's document — the LRAA disinfection byproducts, the PFAS levels, the pesticide non-detects — describes water at the treatment plant or across the whole distribution system, not a reading taken at any one house. The Cary-purchase disclosure makes the point sharply: some of "Durham's water" in a given year wasn't even treated at Durham's own plants.

Two Durham addresses on the same system can see different results at the actual tap, depending on pipe age, distance from the plant, and how long water sits before use. A report built to describe an entire city was never going to answer a question specific to one address — only a test run at that address does that.

What Should a Durham Homeowner Actually Do With This Report?

Read it for what it's good at: source, disinfection byproducts, PFAS, and pesticide monitoring, all measured against real legal limits, all currently compliant. Then treat the two gaps as your actual to-do list — the hardness number the report never states, and the tap-level reading it structurally can't provide. A free water analysis settles both in one visit, and it's exactly what sizing an all-in-one softening-and-carbon system for your address requires.

FAQ

I just moved to Durham and got my first water quality report in the mail — what should I actually look for? Start with the source line — Lake Michie and Little River Reservoir, treated at the Williams and Brown plants — then the disinfection byproduct figures, TTHM and HAA5, compared to their legal limits. Skip looking for a hardness number; Durham's report doesn't include one, so a home hardness test is the only way to get that figure.

My Durham report lists an "LRAA" instead of a plain average — what does that actually mean? LRAA stands for Locational Running Annual Average, the average of four quarters of testing at one specific monitoring point rather than the whole system blended together. Durham reports the highest LRAA for TTHM and HAA5, which is the more conservative figure — it reflects the worst-tested location, not a system-wide smoothing.

Does Durham's report say anything about pesticides in the water? Yes — it includes an explicit table naming atrazine and simazine, sampled quarterly through 2025, and both came back non-detect, well under their respective 3 ppb and 4 ppb limits. Naming the compounds and showing the result, instead of omitting the line entirely, is a genuinely thorough disclosure.

I've heard Durham's water has "forever chemicals" — is that in the report? Yes, and the report is direct about it: PFOA at up to 5.7 ppt and PFOS at up to 7.2 ppt, both monitored with no violations. An activated carbon stage certified for PFAS reduction removes both compounds at your own tap.

Why doesn't my Durham water report list a hardness number the way some other towns' reports do? Hardness isn't a federally regulated contaminant, so Durham's report has no requirement to include it — and after reading the current report in full, it doesn't. Our own testing across the service area measures 1.6 to 3.7 gpg by address, which is the number a hardness decision should actually be based on.

Where can I find Durham's actual water quality report online? The City of Durham publishes it on its own Water Quality Report page — see the Sources section below for the direct link.

See What Your Own Durham Tap Actually Shows

Durham's report never states a hardness figure at all — not a system average, not a range, nothing — so an address-level test is the only way to actually get one. Take the 60-second water quiz or request a free water analysis to find out your Durham address's real hardness number and what's actually reaching your own tap.

Sources

• City of Durham — Water Quality Report
• EPA — National Primary Drinking Water Regulations

Related reading: Water Softener Company in Durham, NC | Trihalomethanes in Tap Water | Haloacetic Acids in Drinking Water | PFAS & Forever Chemicals in Durham, NC | How to Read Your Water Quality Report