Our water

Chlorine byproducts form when chlorine meets the natural organic matter in river and lake water. A living filter — a bed of sand, or the ground beside a river, where bacteria feed on that organic matter — takes out part of it before treatment starts. Biology makes the first cut; the plant finishes the job with less to fight.

Why here: Hot Springs runs closest to the line: its 2025 report shows trihalomethanes at a highest running average of 74 ppb against a limit of 80, with single readings up to 104. Hot Springs — 2025 Annual Drinking Water Quality Report

The evidence:

• At four U.S. riverbank-filtration sites, dissolved organic carbon — what byproducts form from — fell 55% on average (12% to 93% across samples). About 25 points of that came from the living filter underground; the rest from mixing with groundwater. Journal AWWA, 2007 — riverbank filtration at four U.S. sites
• Slow sand filters, where a living layer does the work, remove up to 15–25% of dissolved organic carbon, up to half of the part bacteria can eat, and up to 20–30% of the ingredients that form trihalomethanes. A version with a layer of activated carbon inside the sand removes more. National Environmental Services Center — slow sand filtration
• Federal rules already require plants like these to remove a set share of organic carbon, depending on the water. A living first stage helps meet that. 40 CFR 141.135 · EPA — disinfection byproduct rules

The honest limits:

• A living filter alone isn’t enough. Chemical treatment with activated carbon removes more byproduct-forming matter (a trade source reports 75–80%). This is a first stage, not a replacement.
• Results swing widely from site to site. Riverbank filtration needs the right sand and gravel beside the river.
• It takes land, and a pilot test before anything is built.
• Engineers can also cut byproducts by changing where or how water is disinfected. The right mix is a design question for the utility.

Water Online

First step: A pilot at the Lakeside or Ouachita plant: a small biological or slow-sand filter ahead of treatment, measuring organic carbon and byproducts before and after. The sources are lakes, so riverbank filtration doesn’t apply.

Weigh in on the open question →

Smart meters plus listening devices on the pipes find leaks early. Every gallon lost was already pumped and treated. Hot Springs, Arkansas cut water it couldn’t account for from 44% to 24%, and found one broken valve wasting about 4 million gallons a day (the meter company’s case study).

Limit: The case study comes from the company that sold the system. Savings depend on how leaky the pipes are to begin with. Xylem case study, Hot Springs

A living layer on the sand or carbon filter eats organic matter and ammonia — with fewer chemicals. Less organic matter means fewer chlorine byproducts later. Slow sand filters work this way. Slow sand filters have run for more than 150 years; several U.S. utilities have converted filters to biological operation.

Limit: It doesn’t remove “forever chemicals” (PFAS) by itself, and slow sand filters need land. Biofiltration review, 2016 · Hazen and Sawyer

Ultraviolet light kills germs without adding a chemical, so less chlorine is needed. Adding hydrogen peroxide under UV (advanced oxidation) breaks down trace chemicals too.

Limit: Some chlorine is still needed to keep water safe inside the pipes. Trojan Technologies

Wells beside a river pull water through natural sand and gravel, which filters it before it reaches the plant. Louisville Water in Kentucky uses riverbank filtration.

Limit: Only works where the ground next to the river is the right kind of sand and gravel — that takes a study. Louisville Water

Very fine filters physically block germs and particles. Packaged systems are sold for small towns.

Limit: Membranes need cleaning and replacing, and they use electricity. AMTA

Activated carbon, ion exchange, and reverse osmosis remove PFAS. Destroying PFAS completely (supercritical water, electrochemical methods) is still in pilots.

Limit: EPA set PFAS limits in 2024. In 2026 it proposed pushing the main deadline from 2029 to 2031 and dropping limits for four of the six chemicals — both still proposals. Test first, then decide. EPA · PFAS destruction review · EPA — proposed extension · EPA — proposed rescission

Keeping the watershed healthy — forests, stream banks, fixing upstream sewage — is usually cheaper than treating dirty water. New York City protected its Catskill watershed instead of building a filtration plant estimated at up to $10 billion.

Limit: New York’s dollars don’t scale down; the idea does. PERC

Planted, shallow basins where plants, soil, and microbes clean treated wastewater further. EPA guidance calls them well suited to small towns “where inexpensive land is available.”

Limit: Needs land, and works slower in cold weather. Univ. of Arizona, summarizing EPA guidance

Algae grow on belts that rotate through lagoon water, pulling out phosphorus and nitrogen. The harvested algae can become fertilizer. Gross-Wen Technologies (Iowa) — at least eight systems running in Iowa and Illinois.

Limit: Still young, and algae slow down in winter. Iowa State · phys.org, 2023

Floating plants, fungal filters, and greenhouse ecosystems that clean water. Duckweed pulled more than 93% of nitrogen and phosphorus from wastewater in a study.

Limit: Strong study results, few full-size town plants to copy. Treat as a supplement, not a whole plant. Duckweed study (MDPI) · Oberlin’s Living Machine

Digesting sludge makes biogas; phosphorus can be recovered as a fertilizer. Tigard, Oregon became the first U.S. plant to recycle nutrients into commercial fertilizer (Ostara, 2009).

Limit: Usually pays off only at bigger plants. Ostara

Engineered surfaces that soak up sunlight to evaporate and purify water.

Limit: Researchers say fouling, cost, and scale still need to be solved. No utility runs it. research review · J. Mater. Chem. A, 2022

Ultra-thin carbon membranes that could filter faster with less energy.

Limit: Research says most use is “still limited to laboratory scale.” No U.S. water utility uses them as its main filter yet. ACS Environmental Au review