The cleanest water in a purely chemical sense is distilled water, which can reach a total dissolved solids (TDS) level close to 0 milligrams per liter. That means virtually nothing is left in it besides H₂O molecules. But “cleanest” and “best to drink” aren’t the same thing, and the distinction matters more than most people realize.
How Water Purity Is Measured
The standard way to gauge how clean water is involves measuring total dissolved solids, or TDS, in parts per million (ppm). This number captures everything dissolved in the water: minerals, salts, metals, and chemical compounds. The EPA recommends a maximum of 500 ppm for drinking water, but that’s an upper boundary, not an ideal. A TDS between 300 and 500 ppm is generally considered the sweet spot for drinking water because it retains beneficial minerals like calcium and magnesium without tasting flat or carrying harmful levels of contaminants.
Below 50 ppm, water starts losing the minerals your body actually uses. Above 1,000 ppm, it’s not recommended for drinking. Above 2,000 ppm, household filters can’t adequately clean it.
TDS alone doesn’t tell the whole story, though. Water with a low TDS could still contain bacteria, viruses, or synthetic chemicals like PFAS at dangerous concentrations. That’s why regulators set limits on specific contaminants rather than relying on a single number.
What Makes Distilled Water So Pure
Distillation boils water into steam, then condenses the steam back into liquid. Because contaminants have different boiling points than water, they get left behind. The result is water with a TDS as low as 1 to 5 ppm, removing over 99% of dissolved solids, bacteria, viruses, and minerals. The heat involved in the process kills pathogens outright, which gives distillation an edge over some filtration methods that can let microbes slip through.
Ultra-pure water used in laboratories and semiconductor manufacturing takes this even further, stripping out essentially every detectable ion. It’s the “cleanest” water humans can produce, but it’s engineered for industrial precision, not for drinking.
Why the Cleanest Water Isn’t the Healthiest
Drinking only distilled or demineralized water comes with real downsides. The World Health Organization has flagged several concerns: it can increase urine output and disrupt your electrolyte balance, it doesn’t replace the sodium and minerals you lose through sweat, and long-term consumption may reduce your intake of key nutrients like calcium and magnesium. A 2022 review reinforced these findings, linking prolonged use of demineralized water to lower overall nutrient quality in the diet.
There’s also a practical problem. Most people find ultra-pure water tastes flat and unappealing, which can lead to drinking less water overall. Your body needs minerals dissolved in water, and getting them from your tap is one of the easiest, most passive ways to maintain that balance.
How Tap Water Compares
Municipal tap water in the U.S. is regulated under the EPA’s National Primary Drinking Water Regulations, which set enforceable limits on more than 90 contaminants. Arsenic, for instance, is capped at 10 parts per billion. Lead triggers action if more than 10% of household samples exceed 0.010 milligrams per liter. Turbidity (cloudiness) must stay at or below 0.3 nephelometric turbidity units in at least 95% of monthly samples.
In 2024, the EPA established its first legally enforceable limits for PFAS, the persistent synthetic chemicals found in nonstick coatings and firefighting foam. PFOA and PFOS, the two most studied PFAS compounds, are now capped at 4.0 parts per trillion each, with a safety goal of zero. These limits were confirmed in May 2025.
One area where tap water often outperforms bottled water is microplastics. Research from Ohio State University found that bottled water contained three times as many nanoplastic particles as treated tap water. The plastic packaging itself appears to be a significant source of contamination.
Filtration Methods and What They Remove
If you want cleaner water at home, the right filter depends on what you’re trying to remove.
- Activated carbon filters (including pitcher filters and faucet attachments) excel at removing chlorine taste and odor, volatile organic compounds, and disinfection byproducts. The EPA reports removal efficiencies up to 99.9% for many organic chemicals. They won’t significantly reduce dissolved minerals or salts.
- Reverse osmosis (RO) systems push water through a membrane that blocks 90 to 99% of contaminants, including salts, heavy metals, and most chemicals. They typically reduce TDS to very low levels. RO may not be fully effective against all bacteria and viruses, though most municipal water is already disinfected before it reaches your home.
- Ion exchange filters come in two types. Anion exchange targets negatively charged contaminants like arsenic, nitrate, PFAS, and uranium. Cation exchange softens water by removing calcium and magnesium, along with barium and radium.
- UV treatment uses ultraviolet light to kill or inactivate microorganisms without adding chemicals. It’s highly effective against parasites like Giardia and Cryptosporidium at relatively low doses. Viruses require higher UV doses and are harder to fully eliminate, particularly adenovirus, which is unusually resistant. UV does nothing to remove dissolved chemicals or particles.
No single technology removes everything. RO paired with an activated carbon pre-filter covers the broadest range of contaminants for home use. Adding a UV stage handles any remaining microbial concerns.
The Cleanest Water You Should Actually Drink
The cleanest water that’s also good for you falls somewhere between ultra-pure and untreated. You want water that’s free of pathogens, heavy metals, PFAS, and organic pollutants, but that still contains a healthy mineral content in the 300 to 500 ppm TDS range. Well-treated municipal water meets this standard for most people. If your local water report shows elevated levels of specific contaminants, a targeted filter addresses the gap without stripping out everything beneficial.
If you use reverse osmosis or distillation at home, some systems include a remineralization stage that adds calcium and magnesium back into the water after purification. This gives you the contaminant removal you want without the flat taste or mineral depletion that comes with drinking ultra-pure water long term.