Knightdale, NC Water Is EPA-Compliant and Flagged by EWG — How Both Can Be True

Triangle Waterworks · informational guide

Direct answer: Knightdale's water, supplied by Raleigh Water, is legally compliant with EPA's TTHM and HAA5 limits per the 2025 CCR (up to 42.8 and 33.6 ppb against limits of 80 and 60). A separate EWG database lists Raleigh's HAA9 at 19.9 ppb and TTHM at 21.7 ppb against its own, far stricter non-regulatory guideline. Different bars, different years — both verified, and a carbon stage removes what either one measures.

Why does one source say Knightdale's water is compliant and another says it's flagged?

Because "compliant" and "flagged" answer two different questions against two different bars. Raleigh Water's 2025 Consumer Confidence Report — the utility Knightdale is served through — measures against EPA's legal Maximum Contaminant Levels: 80 ppb for TTHM, 60 ppb for HAA5. Every reading in that report sits under those numbers, so the system is in full compliance.

The Environmental Working Group's Tap Water Database is a separate project entirely. It compares utility data against EWG's own non-regulatory health guidelines, which are set far below EPA's legal limits and aren't a legal standard anything is required to meet. A number that clears EPA's bar can still sit well above EWG's.

What exactly does EWG's database say about this water?

EWG's dataset lists Raleigh Water's HAA9 at 19.9 ppb and its TTHM at 21.7 ppb. Those figures come from an earlier compilation than Raleigh's current 2025 CCR, and it's worth being precise about that: they aren't fabricated, wrong, or contradicted by the newer numbers — they're a different dataset from a different year, verified in their own right.

Both figures matter for different reasons. The TTHM number is directly comparable to the CCR's TTHM figure, just from an earlier year. The HAA9 number is where the real "two bars" story is, because HAA9 isn't the same measurement as HAA5 at all.

Wait — HAA9 and HAA5 aren't the same thing?

No, and this is the detail that resolves most of the confusion. HAA5 is the five haloacetic acids EPA regulates, with a legal MCL of 60 ppb — that's the number on Raleigh Water's CCR. HAA9 is EWG's own nine-compound sum, a broader composite that includes those five plus four more.

There is no EPA MCL for HAA9. It has never been assigned a federal legal limit, so a HAA9 reading can't be described as "compliant with EPA limits" — there's no such limit for it to comply with. EWG instead measures HAA9 against its own internally set guideline, a non-regulatory number chosen well below what EPA considers actionable.

So which one should I actually pay attention to?

Both, for what each one tells you. HAA5 against its MCL tells you whether Knightdale's water meets the legal floor every utility in the country has to clear — and it does. HAA9 against EWG's guideline tells you where the same water sits against a stricter, precaution-oriented benchmark that isn't law anywhere.

Neither number is wrong, and neither cancels the other out. For a nearby comparison of how large that gap between guideline and legal limit can run, Cary's own EWG figures show its HAA9 reading landing roughly 458 times its guideline — an illustration of how far below EPA's ceiling EWG sets its own bar, not a Knightdale-specific figure. Raleigh's HAA9 sits on that same non-regulatory scale.

Does EPA's legal limit mean these compounds are actually safe to drink long-term?

"Legally compliant" answers only one of the two bars — it says a reading stayed on the right side of the number EPA chose, not that the reading is nothing. EPA's National Primary Drinking Water Regulations table lists the potential health effects from long-term exposure above that legal bar: for TTHMs, "liver, kidney or central nervous system problems; increased risk of cancer." For HAA5, "increased risk of cancer."

Those effects describe exposure above the MCL, over years — not a single reading from Knightdale's current, compliant supply. The honest framing keeps both facts: the water clears the legal bar, and the legal bar exists because these are the exact compounds and effects EPA had in mind when it drew the line. A carbon stage removes them outright rather than counting on the line to hold.

Two bars, one table

Four rows, two real bars, one water system. For the underlying chemistry of how both compound families form in the first place, see what TTHM and HAA5 disinfection byproducts are in Triangle NC water. For the trihalomethane compound family specifically, see what are trihalomethanes in your tap water; for the haloacetic acid family, what are haloacetic acids in drinking water.

Does any of this change what Knightdale should actually do?

Not really — the practical answer is the same regardless of which bar a household weighs more heavily. Activated carbon adsorbs TTHM and HAA5/HAA9 alike as water passes through, because the mechanism doesn't care which threshold a compound is measured against. It removes what's physically present.

That's the case for a carbon filtration stage even for a fully compliant utility: it doesn't require picking a side between EPA's ceiling and EWG's guideline. It just takes the compounds out. Paired with softening resin in an all-in-one system, the same install also handles the hardness Knightdale sees, since Knightdale draws from Raleigh Water's system the same way Zebulon and Wendell do.

See where your own Knightdale tap lands

A system-wide CCR average and an aggregator's guideline both describe Raleigh Water in general — neither one is a reading from a specific Knightdale kitchen faucet. Take the 60-second water quiz to see which all-in-one system fits your home, or book a free water analysis to find out what's actually coming out of your own tap. For what a Knightdale home's water treatment plan looks like start to finish, see water treatment in Knightdale, NC.

FAQ

I looked up my water on two different websites and got two different verdicts — is one of them lying? No — neither is lying. One is likely comparing your utility's numbers to EPA's legal limit (which it meets), and the other to a stricter non-regulatory guideline from a group like EWG (which it can still exceed). Both readings can be accurate at the same time because they're measuring against different bars, not disagreeing about the underlying data.

My neighbor said Knightdale's water tested "hundreds of times over" some limit — is that the EPA limit? No, and that distinction matters. That kind of multiple typically refers to a non-regulatory guideline set far below EPA's legal Maximum Contaminant Level, not the MCL itself. Knightdale's water, through Raleigh Water, meets every EPA MCL that applies to it — the larger multiple comes from comparing against a separate, much stricter benchmark.

What's the actual difference between HAA5 and HAA9? HAA5 is the five haloacetic acids EPA regulates, with a legal limit of 60 ppb. HAA9 is a broader nine-compound sum used by aggregators like EWG that includes those five plus four more — and it carries no EPA limit at all, so it can't be described as "compliant" or "non-compliant" with a federal standard.

Is Raleigh Water's 2025 report more trustworthy than the older EWG numbers? Both are verified, real data — they're just from different years and different testing programs, so a direct year-over-year comparison isn't apples-to-apples. The 2025 CCR is the utility's own current primary-source report; the EWG figures reflect an earlier compilation. Neither one is fabricated or wrong.

Does a carbon filter actually care which of these numbers is "the real one"? No. Activated carbon removes TTHM and haloacetic acid compounds by physically adsorbing them as water passes through, regardless of which threshold — EPA's MCL or EWG's guideline — they're being measured against. That's the practical answer underneath the whole comparison.

Should I be more worried about Knightdale's water than a town where I've only seen the EPA numbers? Not necessarily — most Triangle towns would show a similar gap if checked against both an EPA limit and an EWG guideline, since the two are designed to sit at very different thresholds. What's worth acting on isn't which bar looks scarier, but that a carbon stage addresses the underlying compounds either way.

Sources

• City of Raleigh Water — 2025 Consumer Confidence Report
• EPA — National Primary Drinking Water Regulations