You turn on your tap. The water looks clear, tastes fine. But it might contain chemicals that never break down in nature or in your body. Per- and polyfluoroalkyl substances, or PFAS, have contaminated drinking water supplies across the country. When that happens, someone has to pay for the damage. That someone is usually the company that made or used these chemicals. The legal questions are straightforward: Did they know the stuff was dangerous? Did they dump it anyway? And how do you prove they are liable?

PFAS are called forever chemicals because they do not degrade. They have been used since the 1940s in nonstick cookware, waterproof clothing, firefighting foam, and countless industrial processes. They seep into groundwater from landfills, military bases, and factories. Once in the water, they accumulate in human blood. Studies link them to kidney cancer, thyroid disease, high cholesterol, and developmental problems in children. When a water utility tests positive for PFAS above the new federal limits, the utility has to install expensive filtration systems or find new sources. Those costs run into the millions. Someone has to foot the bill, and that someone should be the polluter.

The legal basis for holding companies liable for PFAS contamination rests on several old, solid legal theories. First is nuisance. A private nuisance occurs when someone uses their property in a way that interferes with your use of your property. If a factory’s waste seeps into the aquifer that supplies your well, that is a classic nuisance. Public nuisance applies when the contamination affects a whole community’s water supply. Courts have long recognized that polluting a shared water source is a public nuisance. You do not need a contract or a special relationship. You just need to show that the defendant’s conduct unreasonably interfered with a public right, like the right to clean water.

Second is trespass. Trespass is the physical invasion of your land. PFAS molecules moving through groundwater into your property count as a physical invasion. Courts have held that invisible contaminants can be trespass if they cause actual harm. No one has to see the chemicals. The test is whether the particles entered your land without permission and caused damage. If a company’s PFAS plume travels under your house and into your well, that is trespass.

Third is negligence. To prove negligence, you must show the company had a duty to avoid contaminating your water, it breached that duty, and the breach caused your injury. The duty is easy to establish. Manufacturers of toxic chemicals have a duty to handle them safely. They also have a duty to warn downstream users. When a company knew PFAS were toxic in the 1970s, as internal documents from DuPont and 3M later showed, and still discharged them into rivers and landfills, that is a clear breach. The causation link requires showing that the PFAS in your water came from the defendant’s site. That is often done with forensic hydrogeology and chemical fingerprinting. The chemicals themselves can be traced because different manufacturers use slightly different formulations.

Proving these theories in court is not easy. The polluters have deep pockets and good lawyers. They will argue that PFAS are everywhere now, so you cannot prove yours came from their plant. They will argue that the government set a safety limit only recently, so the chemicals were not known to be harmful before. They will argue that the statute of limitations has run out, meaning you waited too long to sue. But courts have rejected most of these defenses. The discovery rule says the clock does not start ticking until you knew or should have known about the contamination and its cause. For many communities, that happened only after the media or the EPA flagged the issue.

Another major liability route is the Comprehensive Environmental Response, Compensation, and Liability Act, known as Superfund. This federal law allows the government or private parties to force polluters to clean up hazardous waste sites. PFAS are now classified as hazardous substances under Superfund. That means the companies that made or disposed of PFAS can be held strictly liable. Strict liability means you do not need to prove negligence. If you sent the chemicals to a landfill and they leaked, you pay. The law also allows for joint and several liability. If multiple companies contributed to the mess, each can be held responsible for the entire cleanup cost. Then they fight among themselves to allocate shares. That is their problem, not yours.

The practical result for homeowners and water utilities is that they have leverage. They can sue for the cost of filtration systems, medical monitoring, property damage, and sometimes punitive damages if the company acted with malice or reckless disregard. Many cases have already settled for hundreds of millions of dollars. In 2023, 3M agreed to pay over $10 billion to settle PFAS claims from water utilities. DuPont and its spinoffs reached billion-dollar settlements as well. These settlements did not require the companies to admit wrongdoing, but the money went to clean up the water.

If you are affected by PFAS contamination, the first step is to get your water tested. The EPA has established health advisory levels and enforceable limits for six PFAS compounds. If your test comes back above those levels, contact a lawyer who handles environmental litigation. Do not wait. Courts are already seeing a flood of cases, and the earliest filers often get the best settlements. The law is on your side, but only if you use it.