When you fill a glass at the kitchen tap, you expect water and nothing else. In most of the U.S., tap water is safe by the legal standard. But the legal standard doesn’t cover everything that ends up in our water, and some of what it doesn’t cover has been found in drinking water supplies across the country.

What researchers have found

In a national study published in 2002, the U.S. Geological Survey sampled 139 streams in 30 states and found organic wastewater contaminants in 80% of them. These included human and veterinary drugs, hormones, insecticides and fire retardants.

In 2008, an Associated Press investigation found pharmaceuticals, including antibiotics, anticonvulsants and mood stabilizers, in the drinking water supplies of 24 major metropolitan areas serving at least 41 million Americans. The amounts were tiny, measured in parts per billion or trillion. But most water treatment isn’t designed to remove them, and nobody knows the effect of drinking low doses for a lifetime.

That finding alone was enough for my family to improve the filtration of our own water.

What the rules cover, and what they don’t

The EPA sets legal limits for more than 90 contaminants in drinking water. Pharmaceuticals aren’t among them. Some newer concerns are only now being regulated. In 2024 the EPA set the first national limits for PFAS (“forever chemicals”), including 4 parts per trillion for PFOA and PFOS.

This isn’t a distant problem. In 2025 testing, eight of the City of Vancouver’s nine wellfields exceeded the federal PFAS limits, and the city is adding carbon treatment at its water stations. Portland is building a filtration plant for its Bull Run supply to meet federal rules on cryptosporidium. Utilities are doing the work, but it takes years. In the meantime, filtration at home gives you control over the water your family drinks.

To see what has been detected in your local supply, search your zip code in the EWG Tap Water Database or read your utility’s annual water quality report.

How home filtration works

  • Whole-home carbon filtration treats water as it enters the house, so every tap and shower gets filtered water. Activated carbon reduces chlorine, many chemicals and some PFAS.
  • Reverse osmosis (RO) at the kitchen sink pushes water through a very fine membrane and removes a wider range of contaminants, including many dissolved chemicals, metals and pharmaceutical residues. It’s the best choice for drinking and cooking water.

Many families use both: whole-home carbon for showers and laundry, and RO for drinking water.

Choosing a system

Look for systems certified by NSF to the standard that matches your concern. NSF/ANSI 53 covers health-related contaminants such as lead. NSF/ANSI 58 covers reverse osmosis systems. NSF/ANSI 401 covers emerging contaminants, including some pharmaceuticals. A certification tells you the system was tested to do what the box says.

Then keep it maintained. Filters and membranes that are past their replacement date stop working, so follow the manufacturer’s schedule.

Why we plan for it in every home

Adding filtration to an existing home usually means opening walls, rerouting plumbing and adding power. In a new home, it is a few hours of planning. We believe in this strongly enough that every Marnella home is pre-plumbed for both reverse osmosis and whole-home filtration. The space, plumbing and electrical are in place, so either system can go in on move-in day or years later with no demolition. Our 6th St Townhomes are one example.

We cover the plumbing side in efficient HVAC and plumbing design, and why we think these features are worth it in Redefining ROI in Homebuilding.

A clear choice for your new home

Treated tap water is a starting point. Filtration at home adds a layer of protection against the contaminants the rules don’t cover yet. If you are planning a new home, ask your builder to plan for it now, during design and planning, when it costs the least.

Sources: USGS, Kolpin et al., 2002 · Associated Press investigation, 2008 · EPA, PFAS drinking water regulation · City of Vancouver, PFAS mitigation · Portland Water Bureau, Bull Run filtration