Pull the contaminant profile for the public water systems serving Mobile and Baldwin County and one family of compounds dominates. Total trihalomethanes appear on 14 of the 15 systems. Haloacetic acids on 13.
They are also the most misunderstood thing on a water report, because their presence is evidence that the system is working.
Where they come from
Nobody adds TTHMs or HAA5 to water. They form.
Surface water — a river, a reservoir, Big Creek Lake — carries dissolved organic matter: leaf litter, soil, decaying vegetation. When chlorine meets that organic matter, it reacts, and the products of that reaction are trihalomethanes and haloacetic acids.
Which means the by-products are the price of disinfection. Before widespread chlorination, waterborne disease killed people routinely. The trade is real, it is well understood by the people running these systems, and it is not close: a small long-term risk in exchange for the elimination of an immediate one.
Why they are higher here
Two factors compound on the Gulf Coast.
Surface sources carry more organic matter than groundwater. A system drawing from a reservoir starts with more of the raw material.
Warm water speeds the reaction. Formation is temperature-dependent, and this is not a cold climate. The same chlorine dose in the same water produces more by-product in August than in January.
A warm region on surface supplies is close to the worst case, which is why this shows up nearly everywhere in these two counties rather than at one utility.
The numbers locally
The federal limit for TTHMs is 80 ppb, measured as an annual running average across the distribution system.
Local readings span 0.7 to 61.1 ppb, with a median of 6.3. Every system is inside the limit. But the spread is enormous — the highest is nearly ninety times the lowest — and that spread is real information. It tracks source water and distance from the plant more than it tracks how well any utility is run.
Worth knowing: by-product levels rise the further water travels. Chlorine keeps reacting on the journey, so the end of a long distribution line reads higher than a house near the plant, on the same system, from the same water. An average is an average.
What removes them
This is the part with a genuinely clean answer.
Activated carbon. TTHMs and HAA5 adsorb readily onto carbon, which makes them one of the more straightforward things to remove at the point of use. A whole-house carbon filter handles the water you shower in — worth noting, since trihalomethanes are volatile and a hot shower is a real exposure route, not just drinking. An under-sink carbon block or reverse osmosis unit handles what you drink.
Catalytic carbon specifically, where the system uses chloramine rather than free chlorine. Standard activated carbon is much less effective against chloramine, and this distinction is the difference between a filter that works and one that looks like it should.
Not boiling. It is unreliable and can concentrate what stays behind.
The honest framing
If your water report shows TTHMs and HAA5, it shows your water is being disinfected — which is what you want. The question is not whether to have them eliminated at the source; that trade is not on offer and you would not want it.
The question is whether you would rather not drink and shower in them, which is a point-of-use decision, and a cheap one.
You can see the actual by-product readings for your own system alongside its EPA compliance record, or have your tap read directly — because where you sit on the distribution line changes the answer.
Contaminant profiles from the EWG Tap Water Database per PWSID; limits from EPA's National Primary Drinking Water Regulations. Figures current as of 19 August 2026.