Reverse Osmosis Water: Benefits, Risks, and Is It Worth It?

Reverse osmosis (RO) is the most thorough home water filtration method available, capable of removing virtually all contaminants from water. But its thoroughness comes with trade-offs: RO removes beneficial minerals along with contaminants, wastes water, and requires significant maintenance. This guide examines the pros and cons of reverse osmosis water and helps you decide whether an RO system is right for your home.

How Reverse Osmosis Works

Reverse osmosis works by forcing water under pressure through a semi-permeable membrane with pores so small that only water molecules can pass through. Contaminants — including dissolved solids, lead, arsenic, nitrates, fluoride, bacteria, viruses, and most other impurities — are left behind and flushed away as wastewater. The result is extremely pure water, often comparable to distilled water in quality.

A typical under-sink RO system has multiple stages. First, a sediment pre-filter removes particles that could clog the membrane. Second, a carbon pre-filter removes chlorine and organic compounds that could damage the membrane. Third, the RO membrane itself removes dissolved solids and other contaminants. Fourth, a carbon post-filter polishes the water for taste. Some systems add a final stage with a remineralization filter that adds calcium and magnesium back to the water.

RO systems produce water slowly — a typical home system produces 50 to 100 gallons per day, which means about 2 to 4 gallons per hour. To provide water on demand, RO systems include a storage tank that holds 2 to 4 gallons of filtered water. When you turn on the RO faucet, water flows from the tank rather than through the membrane in real time. The tank refills gradually as water is used.

What RO Removes

Reverse osmosis removes a wider range of contaminants than any other home filtration method. According to NSF International, RO systems certified to NSF 58 can remove: lead, arsenic, fluoride, nitrates, nitrites, chromium, cadmium, copper, radium, uranium, barium, selenium, total dissolved solids, cysts (Giardia, Cryptosporidium), bacteria, viruses, PFAS, and many other contaminants. If you have specific contaminants in your water that other filters cannot address, RO is likely the solution.

However, RO also removes beneficial minerals — calcium, magnesium, potassium — that are naturally present in water. The resulting water is "soft" and may taste flat or slightly acidic. Some people prefer the taste of mineral water and find RO water unappealing. To address this, many modern RO systems include a remineralization stage that adds calcium and magnesium back to the water after filtration. If taste is a concern, look for a system with this feature.

RO does not remove all contaminants. Some gases (like chlorine in gas form), some volatile organic compounds (VOCs), and certain pesticides may pass through the membrane. This is why RO systems include carbon pre- and post-filters — to address contaminants that the RO membrane alone cannot. A well-designed multi-stage RO system provides the most comprehensive filtration available for home use.

The Downside of RO

The most significant downside of reverse osmosis is water waste. For every gallon of filtered water produced, a typical RO system wastes 3 to 5 gallons of water (called "brine" or "concentrate") that is flushed down the drain. This is concerning in areas with water scarcity and can increase water bills. Newer, more efficient RO systems have reduced this ratio to 1:1 or even 1:0.5, but they are more expensive. If water conservation is a priority, look for a high-efficiency system.

Another downside is the removal of beneficial minerals. While the minerals in water are a minor source compared to food, some research suggests that long-term consumption of demineralized water may have negative health effects, including increased diuresis (which can lead to electrolyte loss), reduced bone density (due to lower calcium intake from water), and increased risk of cardiovascular disease (due to lower magnesium intake). The evidence is not strong enough to definitively conclude that RO water is harmful, but it is a consideration. A remineralization stage addresses this concern.

RO systems also require maintenance. The pre-filters need replacement every 6 to 12 months, the RO membrane every 2 to 5 years, and the post-filter annually. The storage tank may need sanitizing periodically. If maintenance is neglected, the system can become a breeding ground for bacteria, and water quality will decline. Annual maintenance costs typically range from 50 to 150 dollars.

Is RO Right for You?

RO is the right choice if your water has specific contaminants that other filters cannot remove effectively. If you have arsenic, nitrates, fluoride, PFAS, or high total dissolved solids in your water, RO is likely your best option. If you have a private well with bacterial contamination, RO (with UV treatment) can provide safe drinking water. If you simply want to remove chlorine and improve taste, a simpler carbon filter is sufficient and more economical.

RO is also popular for aquarium owners (fish require very pure water), for people who brew coffee or tea and want to control water chemistry, and for people with specific health concerns who want the purest possible water. If you fall into one of these categories, the investment may be worthwhile. For most people on municipal water that meets safety standards, a simpler filter is usually sufficient.

If you do choose RO, consider a system with a remineralization stage to add beneficial minerals back to the water. Look for NSF 58 certification to verify performance. Plan for the installation (most systems require a hole in the sink for the dedicated faucet and a drain connection for the brine). Budget for annual maintenance. And consider the water waste — if you live in a drought-prone area, a high-efficiency system or a different filtration method may be more appropriate.

Alternatives to RO

If RO is not the right fit, there are alternatives. For most contaminants, a high-quality under-sink carbon filter certified to NSF 53 provides adequate protection at a fraction of the cost and with no water waste. For specific contaminants like fluoride, an activated alumina filter can be effective. For bacteria and viruses, UV treatment is effective and wastes no water. For hard water, a water softener addresses the hardness without removing other contaminants. A water quality test will tell you which contaminants you need to address, and a qualified water treatment professional can recommend the most appropriate and cost-effective solution.

For more on water quality, see our guides to water quality and filtration, water filters buying guide, and hard water vs soft water. For general hydration, use our Daily Water Intake Calculator.