The cleanest drinking water is water that has been purified to remove virtually all contaminants while retaining enough minerals to taste good and support health. Distilled water is technically the purest, removing 99% or more of dissolved solids, bacteria, and chemicals. But “cleanest” in practice means something more nuanced: water that’s free of harmful contaminants, low in microplastics and industrial chemicals, and still pleasant to drink. How you get there depends on your starting source and what you do to treat it.
What “Clean” Actually Means
Water cleanliness is measured in several ways. The most common is total dissolved solids (TDS), a count of everything dissolved in water, from minerals like calcium to contaminants like lead. The EPA and Canadian guidelines both set a recommended TDS limit of 500 parts per million for drinking water. Below that, water generally tastes good. Go too low, though, and water tastes flat and lifeless.
But TDS alone doesn’t tell you whether water is safe. A glass of water could have a low TDS reading and still contain dangerous levels of lead, arsenic, or bacteria. The EPA sets legal limits for over 90 contaminants in public water systems. The maximum allowable level for arsenic is 0.010 milligrams per liter. For lead, if more than 10% of tap water samples in a system exceed 0.010 milligrams per liter, the utility must take corrective action. For disease-causing organisms like Cryptosporidium and Giardia, the goal is zero.
Truly clean water, then, meets two criteria: it’s below harmful thresholds for regulated contaminants, and it’s free of emerging pollutants like PFAS (sometimes called “forever chemicals”) and microplastics that regulations haven’t fully caught up with.
Distilled vs. Reverse Osmosis Water
If you’re after maximum purity, the two most effective methods are distillation and reverse osmosis. Distillation boils water into steam and then condenses it back into liquid, leaving behind 99% or more of dissolved solids, bacteria, viruses, salts, and chemicals. Because it involves heat, it kills pathogens outright. Reverse osmosis forces water through a membrane so fine that it blocks 90 to 99% of contaminants, including heavy metals, salts, and many chemicals.
The practical difference: distillation is more thorough but slower and more energy-intensive. Reverse osmosis is faster and more common in home filtration systems, but it may not catch every bacterium or virus on its own, which is why many RO systems include multiple filtration stages. Both methods strip out beneficial minerals like calcium and magnesium along with the bad stuff. The World Health Organization has studied the health consequences of long-term consumption of demineralized water and raised concerns about mineral deficiency, which is why some systems add minerals back in after purification.
How Tap Water Compares to Bottled Water
Municipal tap water in developed countries goes through extensive treatment and is tested against federal standards. For most people, it’s safe to drink straight from the tap. The bigger question is what happens between the treatment plant and your glass. Old pipes can leach lead. Chlorine used for disinfection can create byproducts. And both tap and bottled water contain microplastics.
On the microplastics front, bottled water consistently performs worse. A review of 21 studies found that microplastic concentrations are higher in bottled water than in tap water, likely because plastic packaging itself sheds particles into the water. The smaller the particles, the more of them there are, and bottled water tends to contain smaller, harder-to-detect fragments. If avoiding microplastics is a priority, tap water filtered at home is a better starting point than most bottled options.
Spring water, often marketed as naturally pure, varies enormously. North American spring waters contain very low mineral levels, with median calcium around 6 milligrams per liter and magnesium around 3 milligrams per liter. Adults get less than 3% of their daily mineral needs from most spring waters. “Spring” on a label tells you where the water came from, not how clean it is.
Which Filters Remove the Most
No single filter handles everything. Different technologies target different contaminants, which is why multi-stage systems exist.
- Granular activated carbon (GAC) excels at removing taste and odor problems, chlorine, organic chemicals, and disinfection byproducts. It’s also one of the EPA-recommended technologies for reducing PFAS levels at home.
- Ion exchange resins target specific charged contaminants. Anion exchange removes arsenic, nitrate, PFAS, and uranium. Cation exchange softens water by pulling out calcium and magnesium.
- Reverse osmosis provides broad-spectrum filtration through a multi-stage process, typically three to five stages, that catches most dissolved chemicals, heavy metals, and salts.
- UV treatment kills bacteria and viruses using ultraviolet light but doesn’t remove chemical contaminants or dissolved solids.
For the cleanest possible result at home, a system combining activated carbon, reverse osmosis, and UV disinfection covers the widest range of threats. If your main concern is PFAS, the EPA found that GAC, ion exchange, and RO point-of-use systems all significantly reduce forever chemical levels. Look for filters certified under NSF/ANSI 53 (which covers health-related contaminants) or NSF/ANSI 58 (which covers reverse osmosis systems). NSF/ANSI 42 covers only aesthetic issues like taste and odor, so it’s not sufficient if you’re worried about lead, arsenic, or PFAS.
The Mineral Balance Question
Ultra-purified water isn’t necessarily the healthiest water. Water that’s been stripped of all minerals tastes flat, and some research suggests that long-term consumption of completely demineralized water could affect mineral balance in the body. The WHO has specifically studied this concern in the context of desalinated and membrane-treated water.
The sweet spot for most people is water with a moderate mineral content: clean enough to be free of harmful contaminants, but not so aggressively purified that it’s lost its calcium and magnesium. If you use an RO or distillation system, a remineralization filter or mineral drops can restore what the purification process removed. Many newer RO systems include a remineralization stage for exactly this reason.
What About Alkaline Water?
Alkaline water, which has a higher pH than regular water, is heavily marketed as healthier and cleaner. The scientific evidence doesn’t support most of those claims. Some animal studies have suggested anti-obesity effects, but human research has produced mixed results, with findings ranging from mildly positive to no effect at all. There is no evidence that alkaline water is “cleaner” than properly filtered neutral water. Your stomach acid neutralizes the alkalinity almost immediately after you drink it. Spending extra on alkaline water for health benefits is not well supported by current science.
The Cleanest Option in Practice
For most households, the cleanest drinking water comes from a well-maintained municipal supply filtered through a certified multi-stage home system. A reverse osmosis unit with an activated carbon pre-filter and a remineralization post-filter covers the broadest range of contaminants, from lead and arsenic to PFAS and chlorine byproducts, while keeping the water palatable and mineral-balanced.
If you’re on well water, testing is the essential first step, since you won’t know what you need to filter without knowing what’s in your water. Focus on the contaminants that matter most for your source: nitrates from agricultural runoff, arsenic from natural deposits, or bacteria from septic systems. Then choose a filtration system certified to address those specific problems. The cleanest water isn’t about buying the most expensive brand or the most extreme purification technology. It’s about knowing what’s in your water and removing what shouldn’t be there.