South Dakota District Detects PFAS but Has No Plan to Remove Them

A South Dakota water district that draws from the Big Sioux River is expanding testing for PFAS, the synthetic compounds known as "forever chemicals," and evaluating treatment options after detecting the contaminants in its source water. The district supplies drinking water to communities across the Sioux Falls metropolitan area, where hundreds of thousands of residents depend on the river as a primary source.

The announcement comes as the EPA has added new substances to its contaminant candidate list for further scientific review, signaling a broader federal push to understand emerging threats in public drinking water. But for the communities along the Big Sioux, the question is more immediate: what is in their water right now, and what will it cost to remove it?

Forever Chemicals Confirmed in the Big Sioux

PFAS, or per- and polyfluoroalkyl substances, are a class of thousands of synthetic chemicals used in nonstick coatings, firefighting foam, food packaging, and industrial applications. They are called "forever chemicals" because they do not break down in the environment and accumulate in water, soil, and human tissue over time.

The water district has confirmed detections of PFAS in the Big Sioux River and is planning additional rounds of testing to determine the scope and consistency of contamination. According to South Dakota Searchlight, officials are now considering whether the district will need to invest in advanced treatment infrastructure capable of filtering the compounds from finished drinking water.

The source of the PFAS in the Big Sioux has not been definitively identified. Rivers can accumulate PFAS from multiple upstream contributors, including wastewater treatment plants, agricultural runoff from biosolids, industrial discharge, and stormwater. In South Carolina, a separate investigation found that state agencies knew for years that PFAS-laden sewage sludge was being applied to farmland, contaminating surrounding water supplies.

Who Relies on the Big Sioux

The Sioux Falls metro area is South Dakota's most populated region, and any contamination in the river has the potential to affect a large share of the state's residents, including vulnerable populations such as infants, pregnant women, and people with compromised immune systems.

PFAS exposure has been linked to increased risks of certain cancers, thyroid disease, immune suppression, and developmental harm in children. Because the chemicals bioaccumulate, even low-level chronic exposure through drinking water raises long-term health concerns. Residents who have been drinking unfiltered tap water sourced from the river may have been exposed for years without knowing it.

No Treatment Timeline Yet

The water district has acknowledged the detections and signaled its intent to address them, but has not committed to a specific treatment timeline or technology. Advanced filtration methods such as reverse osmosis, granular activated carbon, and ion exchange resins are effective at removing PFAS from drinking water, but retrofitting a municipal system carries significant cost.

As of publication, the district has not released detailed sampling data or identified which specific PFAS compounds were detected, or at what concentrations. The EPA finalized national drinking water limits for six PFAS compounds in 2024, setting maximum contaminant levels as low as 4 parts per trillion for PFOA and PFOS. However, enforcement timelines and the future of those standards remain uncertain as the agency undergoes regulatory restructuring.

EPA Adds Microplastics and Pharmaceuticals to Its Watch List

The Big Sioux situation unfolds against a backdrop of expanding federal attention to unregulated drinking water contaminants. The EPA recently released a draft update to its Contaminant Candidate List, adding microplastics and pharmaceuticals for the first time, alongside additional PFAS compounds and the industrial solvent 1,4-dioxane. According to Coastal Review, the listing does not create enforceable limits but signals that formal regulation could follow.

For communities like those along the Big Sioux, the gap between detection and enforceable standards creates a period of uncertainty. Water districts may detect PFAS at levels that concern health experts but fall below thresholds that would legally require treatment. That leaves the decision to invest in filtration infrastructure largely up to local utilities and the communities that fund them.

What This Means for You

If you're in the Sioux Falls area:

• Request your water district's most recent Consumer Confidence Report and ask specifically whether PFAS testing results are included. Many utilities test for PFAS but do not prominently feature the results.
• Consider a point-of-use filter certified to NSF/ANSI 58 (reverse osmosis) or NSF/ANSI 53 (activated carbon) for your drinking and cooking water while the district evaluates treatment options. Our guide to removing forever chemicals from tap water covers which technologies are certified for specific PFAS compounds.
• If you have a private well near the Big Sioux River floodplain, get it tested independently. PFAS from surface water and agricultural runoff can migrate into shallow groundwater.

For general preparedness:

• Test your tap water using a certified lab that screens for PFAS. Home test kits for PFAS are becoming more available, but lab analysis provides the most reliable results. Our water quality testing guide walks through the process.

Filtering PFAS at Home

PFAS reach household taps through treated municipal water when the utility's treatment process does not include advanced filtration stages designed for these compounds. Standard chlorination and sediment filtration, the backbone of most municipal treatment plants, do not remove PFAS.

The most effective household technologies for PFAS removal are reverse osmosis systems certified to NSF/ANSI 58 and activated carbon block filters certified to NSF/ANSI 53. Reverse osmosis forces water through a semipermeable membrane that rejects PFAS molecules, while high-quality activated carbon adsorbs them. Each technology has trade-offs in cost, water waste, and maintenance frequency. Our review of the best reverse osmosis systems for home use covers under-sink and countertop options tested against PFAS compounds.

For households that want whole-home protection or prefer a simpler countertop setup, activated carbon systems offer a lower-cost entry point. Our guide to activated carbon water filters details which models carry the relevant certifications and how filter lifespan varies by contamination level.