Drinking water and purified water differ mainly in how they’re treated and what’s left in them afterward. Drinking water, usually delivered through your tap, goes through municipal treatment to meet safety standards but retains natural minerals and trace amounts of treatment chemicals like chlorine. Purified water undergoes additional processing to strip out nearly all dissolved substances, including those minerals and chemicals.
What Counts as Drinking Water
When most people say “drinking water,” they mean the water that comes out of the tap. Municipal systems collect water from rivers, lakes, reservoirs, or underground aquifers, then treat it to meet federal safety limits set by the Environmental Protection Agency. That treatment typically involves filtering out sediment, disinfecting with chlorine or similar chemicals to kill bacteria, and sometimes adding fluoride for dental health. The finished product still contains dissolved minerals like calcium, magnesium, and trace metals picked up from the source and the pipes it travels through.
These minerals are what give tap water its flavor. Water rich in calcium and magnesium can taste slightly sweet, while water with higher levels of iron or zinc can taste metallic. A high concentration of chloride makes water taste salty, and elevated sulfates can make it bitter. Your tap water’s taste profile depends almost entirely on where you live and how old your local infrastructure is.
Municipal tap water is tested frequently. City water systems are required to test for coliform bacteria 100 or more times per month, and chemical limits are set for dozens of contaminants. That said, tap water isn’t perfect everywhere. Millions of people in the U.S. get water from systems that have detected lead, and contaminants like PFAS, atrazine, and nitrates have been found in drinking water supplies across parts of the country.
What Makes Water “Purified”
Purified water is a broad category that includes any water treated to remove impurities beyond standard municipal processing. Distilled water, reverse osmosis water, and deionized water all fall under this umbrella. The key distinction is that purification aims to remove nearly all dissolved solids, not just the contaminants that pose health risks.
The most common purification methods are reverse osmosis and distillation. Reverse osmosis forces water through a membrane with pores so small that only water molecules pass through, leaving most dissolved salts and chemicals behind. It removes lead, copper, chromium, sodium, and chloride, and can reduce levels of arsenic, fluoride, nitrate, calcium, and magnesium. Distillation works differently: it heats water into steam, then cools the steam back into liquid, leaving dissolved minerals behind as scale. Distillation removes arsenic, barium, cadmium, lead, nitrate, and many organic chemicals.
A third approach, carbon filtration, uses a medium with tiny pores to strain out larger contaminants. It’s common in pitcher filters and fridge filters, though it removes fewer dissolved substances than reverse osmosis or distillation.
Who Regulates Each Type
Tap water and bottled purified water answer to different federal agencies. The EPA regulates public drinking water systems, setting maximum contaminant levels and requiring regular testing. The FDA regulates bottled water, including anything labeled “purified.” FDA rules require bottled water producers to process and bottle under sanitary conditions, protect water sources from contamination, and test both source water and the final product.
The chemical limits for both categories are almost identical, but testing frequency is not. Bottled water producers only need to test for coliform bacteria once a week, compared to 100-plus times per month for municipal systems. And some contaminants regulated in tap water aren’t regulated in bottled water at all. PFAS, for example, are not regulated in bottled water, and independent testing has found several brands contaminated with these chemicals.
Mineral Content and Health
The most meaningful nutritional difference between the two is mineral content. Tap water contains varying levels of calcium, magnesium, and fluoride depending on the source. Purified water, especially reverse osmosis and distilled, has most of these minerals stripped out.
That matters more than you might expect. Calcium and magnesium from drinking water contribute to bone and tooth health, and research published in Cureus found that long-term consumption of low-mineral water, combined with normal mineral excretion, can promote demineralization of bones and teeth. This increases the risk of osteoporosis and dental cavities over time. Fluoride in tap water specifically supports remineralization of tooth enamel. When calcium intake from water is low, the body compensates by pulling from its own reserves to maintain blood calcium levels.
This doesn’t mean purified water is dangerous. Most people get the majority of their minerals from food. But if your diet is already low in calcium or magnesium, relying exclusively on purified water removes one more source.
Taste Differences
Purified water tastes noticeably “flatter” or more neutral than tap water because the dissolved minerals that create flavor have been removed. Some people prefer this clean, blank taste. Others find it bland.
Tap water’s flavor varies widely. If your local water has a metallic edge, that’s likely elevated iron, zinc, or manganese, or a lower-than-normal pH. Chlorine taste comes from the disinfection process and is one of the most common complaints about tap water. A simple carbon filter on your faucet or in a pitcher can reduce chlorine taste without stripping out beneficial minerals, which makes it a middle ground between unfiltered tap and fully purified water.
Cost and Environmental Impact
Tap water costs a fraction of a cent per glass. Bottled purified water costs dramatically more, and roughly 25 percent of bottled water sold is simply repackaged tap water, sometimes with additional treatment and sometimes without.
The environmental cost of bottled water is significant. Millions of tons of plastic bottles end up in landfills, and production itself is water-intensive. It takes about 1.63 liters of water to produce a single liter of some major brands. Beyond the plastic waste, research has found that a liter of bottled water contains roughly 240,000 tiny plastic fragments, making bottled water a major source of microplastic exposure. Plastic bottles can also leach heavy metals and hormone-disrupting chemicals into the water they hold.
A home reverse osmosis system or a quality carbon filter lets you improve your water without the ongoing cost or plastic waste of buying bottles. Home systems range from simple pitcher filters to under-sink reverse osmosis units, and the choice depends on what contaminants you’re trying to address.
Which One Should You Drink
For most people in the U.S., tap water is safe, affordable, and nutritionally better than purified water because it retains minerals your body uses. If you’re concerned about specific contaminants like lead (especially in older homes with lead pipes) or if your local water system has documented issues, a home filtration system targeted to those contaminants is the most practical solution.
Purified water makes sense in specific situations: if your tap water source is compromised, if you need very clean water for medical devices or certain appliances, or if you simply prefer the taste. Just be aware that full purification removes beneficial minerals along with contaminants, and that bottled versions come with microplastic exposure and environmental costs that tap water doesn’t carry.