Reading the TTHM and HAA5 Rows on Your Wake Forest, NC Water Report

Triangle Waterworks · informational guide

Direct answer: Two rows on a Wake Forest water quality report — TTHM and HAA5 — each list an average, a top-of-range figure, and an EPA limit called the MCL. Wake Forest runs on Raleigh Water's system, where the 2025 report shows TTHM reaching 42.8 ppb and HAA5 reaching 33.6 ppb, both under their limits. A carbon filtration stage removes both, which is the other half of an all-in-one whole-home system.

What does "TTHM" actually stand for?

TTHM is short for total trihalomethanes — a summed measurement of four related compounds that form when a disinfectant reacts with organic material still present in source water. It isn't one chemical; it's a family, added together into one number.

That single combined figure is what shows up on the report, rather than four separate lines. Regulators track the sum because the four compounds share a common cause and a common health basis, so summing them gives one workable number to hold utilities to.

What does the MCL column mean?

MCL stands for Maximum Contaminant Level — the legal ceiling EPA sets for a regulated compound in tap water. For TTHM, that ceiling is 80 parts per billion. For HAA5, it's 60 ppb. Any reading under that number means the utility is in compliance.

EPA's own National Primary Drinking Water Regulations table also lists why the ceiling exists in the first place — the potential health effects from long-term exposure above the MCL. For TTHMs, that's "liver, kidney or central nervous system problems; increased risk of cancer." For HAA5, it's "increased risk of cancer."

Those effects describe exposure above the line, over years, not a single glass of Wake Forest's current, compliant water. But a passing grade on the MCL column only means the number stayed under the cutoff EPA chose — it doesn't mean the row reads zero. They're the same compounds a carbon filtration stage is built to remove, rather than leaving the job to a cutoff on a printed page.

Why does the report list an average and a separate range?

Because TTHM and HAA5 levels aren't identical everywhere water travels through the distribution system — they climb the longer water sits in pipes reacting with disinfectant, so a sample taken near the treatment plant reads differently than one taken at the far edge of the system. A single average would hide that spread.

That's why Raleigh Water's 2025 report — the system Wake Forest draws from — publishes both figures. TTHM averages 34.2 ppb but reaches 42.8 ppb at some sampling points. HAA5 averages 22.0 ppb but reaches 33.6 ppb. The range number, not the average, is the one that matters for a household near the higher end of the system.

How is the HAA5 row different from the TTHM row above it?

Both form the same way — chlorine-based disinfectant reacting with organic matter in source water — but they're chemically distinct compound groups with separate detection methods and separate limits. HAA5 covers five specific haloacetic acids; TTHM covers four different trihalomethane compounds.

They're reported on separate lines because EPA regulates them separately, each with its own MCL and its own testing protocol. A report showing both isn't redundant — it's two related but distinct measurements of the same underlying disinfection process.

Is this Wake Forest's own testing, or is it Raleigh's report?

Wake Forest doesn't operate a separate treatment plant for these figures — it's served by Raleigh Water, along with Garner, Knightdale, Rolesville, Wendell, and Zebulon. The TTHM and HAA5 numbers on a Wake Forest resident's report are Raleigh Water's 2025 Consumer Confidence Report figures, not a town-specific reading.

That's not a downgrade — Raleigh Water tests the same distribution system Wake Forest households draw from. For a walkthrough of the rest of that report line by line, see how to read your water quality report in Wake Forest. For the mechanics of why these two compounds form at all, see what TTHM and HAA5 disinfection byproducts are across the Triangle. For the full picture of what a Wake Forest home's water needs beyond these two rows, see water treatment in Wake Forest, NC.

The two rows, side by side

Both rows describe compliant water. Neither row describes zero. A whole-home carbon stage adsorbs both compound groups as water passes through, the same mechanism that pulls chlorine and chloramine taste out of the tap.

Hardness is a separate row entirely

Wake Forest's report also carries a hardness figure, and it's worth not conflating it with TTHM or HAA5 — they come from entirely different chemistry. Raleigh Water's system averages 21.9–35.3 ppm, roughly 1.3–2.1 gpg, which lands as slightly hard on the WQA/Hach scale, never plain "hard" and never "soft" (more on that in is Wake Forest, NC water hard?). What we measure at homes across the wider service area runs 1.6–3.7 gpg depending on ZIP code — a range that spans slightly hard to moderately hard.

A softener addresses that hardness row through ion exchange. It does nothing for the TTHM and HAA5 rows above it — that gap is exactly why the all-in-one system bundles softening resin with a carbon stage rather than shipping either one alone.

Get your own address checked, not just the system average

The two rows on a Wake Forest report tell you what Raleigh Water measured across its whole distribution network — not necessarily what's coming out of a specific tap on a specific street. Take the 60-second water quiz to see which all-in-one system fits a Wake Forest home, or book a free water analysis to get your own household's numbers rather than a system-wide range.

FAQ

I just got my first Wake Forest water report and don't understand the TTHM/HAA5 rows — where do I even start? Start with the MCL column next to each number — that's the legal ceiling, 80 ppb for TTHM and 60 ppb for HAA5. Then check whether the reading is the average or the range figure; Wake Forest's Raleigh Water system reports both, and the range (42.8 and 33.6 ppb) is the more conservative number to pay attention to.

Why does my report say "Raleigh Water" when I live in Wake Forest? Because Wake Forest doesn't run its own separate water treatment system for these figures — it's supplied through Raleigh Water, the same as Garner, Knightdale, Rolesville, Wendell, and Zebulon. The TTHM and HAA5 numbers you're reading are that shared system's 2025 report.

Are TTHM and HAA5 the same thing listed twice under different names? No. They're two separate compound families that both form from disinfectant reacting with organic matter, but they're chemically distinct, tested separately, and carry their own EPA limits — 80 ppb for TTHM, 60 ppb for HAA5.

If both numbers are under the MCL, does that mean my water is completely clean of them? No — under the MCL means legally compliant, not zero. The compounds are present at real, measured levels; the MCL is simply the cutoff line EPA drew for what it will and won't allow. A carbon filtration stage removes what's actually present rather than just keeping the printed number on the right side of that line.

Does the hardness number on the same report have anything to do with TTHM or HAA5? No, they're unrelated. Hardness comes from dissolved calcium and magnesium; TTHM and HAA5 come from disinfectant reacting with organic material. A softener only addresses the hardness row — only carbon filtration addresses the two disinfection-byproduct rows.

Can I just boil my Wake Forest tap water to get rid of TTHM and HAA5 before I understand all this? Boiling is a response to microbial contamination, not to water chemistry, so it isn't the tool for these two compound groups. Activated carbon is the established method for reducing them, and it's the same stage built into an all-in-one whole-home system.

Sources

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