Reverse osmosis water is safe to drink and exceptionally clean, but it comes with a tradeoff: the same process that strips out harmful contaminants also removes beneficial minerals your body uses every day. For most people eating a balanced diet, this isn’t a serious problem. But if RO water is your primary drinking source, the mineral gap is worth understanding.
What RO Actually Removes
Reverse osmosis pushes water through a semipermeable membrane with pores so small that most dissolved substances can’t pass through. The result is water with very few total dissolved solids. Residential-grade RO systems remove up to 99% of lead, over 90% of PFAS (including harder-to-capture short-chain varieties), and a long list of other contaminants: arsenic, mercury, cadmium, chromium, nitrates, fluoride, radium, uranium, pesticides, and microplastics. It also filters out protozoan parasites like Cryptosporidium.
That makes RO one of the most thorough filtration methods available for home use. If you live in an area with aging pipes, agricultural runoff, or known contamination, an under-sink RO unit (typically around $280, with yearly filter replacements costing about $90) can meaningfully reduce your exposure to harmful substances.
The Mineral Removal Problem
Here’s where the picture gets more complicated. RO doesn’t distinguish between harmful dissolved substances and helpful ones. It strips out calcium, magnesium, potassium, and other minerals along with everything else. The World Health Organization has specifically noted that point-of-use RO devices produce water “devoid of all minerals,” and that long-term consumption of very low-mineral water can disrupt the body’s mineral and water balance. In WHO research, drinking demineralized water was associated with increased urine output and greater excretion of important minerals from the body, essentially pulling minerals out rather than putting them in.
Calcium and magnesium are the two minerals that matter most here. Inadequate calcium intake is linked to higher risks of osteoporosis, kidney stones, and high blood pressure. Low magnesium is connected to poor blood sugar regulation, increased inflammation, and cardiovascular problems. Multiple large-scale studies have found that people who drink harder water (water naturally rich in calcium and magnesium) tend to have lower rates of cardiovascular death. Several researchers have suggested that drinking water should contain at least 20 to 30 mg/L of calcium and 10 mg/L of magnesium to provide a protective benefit.
To be clear, drinking water isn’t your main source of these minerals. Food is. But for people whose diets are already marginal in calcium or magnesium, losing even the modest contribution from tap water can tip the balance in the wrong direction. The WHO’s expert panel recommended that demineralized water contain a minimum of 100 mg/L of total dissolved salts and at least 30 mg/L of calcium.
RO Water Is Slightly Acidic
Without its mineral content, RO water typically has a pH between 6.0 and 6.5, making it mildly acidic compared to regular tap water (which usually falls between 7.0 and 8.5). This isn’t dangerous to drink. Your body tightly regulates blood pH regardless of what you consume. But there’s a practical concern: demineralized water is corrosive to plumbing. The WHO has warned that unstabilized demineralized water can leach metals like copper and lead from pipes, potentially reintroducing the very contaminants you were trying to avoid. If your home has older copper or lead-soldered pipes, this is worth considering.
Fluoride and Dental Health
RO systems remove between 50% and 85% of fluoride from water, depending on the membrane. If your municipal water is fluoridated to prevent tooth decay, an RO system will likely drop the fluoride concentration below the 0.6 ppm threshold where dental benefits are observed. For adults, this is a minor issue since fluoride toothpaste provides most of the protection. For young children whose teeth are still developing, the American Academy of Pediatric Dentistry recommends fluoride supplements when drinking water falls below 0.6 ppm.
Adding Minerals Back
Many newer RO systems include a remineralization stage that adds calcium and magnesium back into the filtered water. These cartridges use small mineral balls or mineral-infused carbon filters to dissolve trace amounts of beneficial minerals as water passes through. The concentrations added back are lower than what you’d find in naturally hard tap water, but they improve taste and bring the pH closer to neutral. If you’re buying or upgrading an RO system, a remineralization cartridge is a worthwhile addition.
You can also remineralize manually by adding mineral drops to your water or keeping a small amount of mineral-rich salt (like Himalayan pink salt) in your routine. Another option is simply making sure you’re eating enough mineral-rich foods: dairy, leafy greens, nuts, seeds, and legumes cover both calcium and magnesium well.
Water Waste to Consider
RO systems produce wastewater as part of the filtration process. For every gallon of purified water, older systems could send three or four gallons down the drain. Newer high-efficiency models have improved significantly, with many achieving a 1:2 ratio (one gallon of waste per two gallons of clean water). The most aggressive water-saving models claim a 1:1 ratio, though real-world performance varies. EPA’s WaterSense specification caps waste at about 2.3 gallons per gallon of treated water. If water conservation matters to you, look for systems that meet or exceed that standard.
Who Benefits Most From RO Water
RO water makes the most sense when your source water has a known contamination issue. If you’re on a well with high nitrates or arsenic, living in a home with lead service lines, or in an area with detectable PFAS levels, an RO system provides a level of protection that standard carbon filters can’t match. It’s also commonly used by people with compromised immune systems who need extra assurance against microbial contamination.
If your municipal water is already clean and well-regulated, the benefits are smaller, and you’re mainly trading mineral content for extra purity. In that case, a quality carbon filter may be a simpler solution that retains beneficial minerals while still improving taste and removing chlorine, some pesticides, and volatile organic compounds. For those who do choose RO, pairing it with a remineralization cartridge and maintaining a mineral-rich diet addresses the main nutritional concern.