What's Bad About Reverse Osmosis? Uncovering the Full Picture

December 21, 2025 •

3 min read

According to the U.S. Environmental Protection Agency (EPA), many traditional reverse osmosis (RO) systems can waste several gallons of water for every single gallon they purify. This significant inefficiency is just one of several critical factors to consider when evaluating what's bad about reverse osmosis water filtration.

Quick Summary

Reverse osmosis offers ultra-pure water, but comes with notable drawbacks, including significant water wastage, the removal of essential minerals, increased energy costs, and a slower filtration process.

Key Points

Water Wastage: RO systems produce a significant amount of wastewater, though newer, high-efficiency models are mitigating this issue.
Mineral Stripping: The process removes beneficial minerals like calcium and magnesium, which can be addressed with a remineralization filter.
Increased Acidity: RO water can have a lower, more acidic pH, which may cause it to be corrosive to plumbing over time.
Higher Costs: Initial installation is more expensive, and ongoing costs for filter and membrane replacements are required for proper maintenance.
Slower Production: RO systems filter water slowly, necessitating a storage tank for on-demand access, which can be a nuisance.
Potential Health Debates: While effective at purification, long-term consumption of demineralized water is a debated health concern, particularly for those with already poor nutrition.
Maintenance Requirements: Regular filter changes and upkeep are essential to prevent microbial buildup and ensure the system functions correctly.

Understanding the Drawbacks of Reverse Osmosis

While reverse osmosis (RO) is a highly effective method for removing a vast array of contaminants from water, it is not without its limitations. For homeowners, industrial users, and health-conscious individuals, understanding the full scope of its disadvantages is crucial before investing in an RO system. The downsides range from environmental and economic impacts to potential health considerations and performance issues.

The Environmental Burden of Water Wastage

One of the most frequently cited criticisms of reverse osmosis is its high water wastage. The cross-flow filtration process flushes rejected impurities to the drain as wastewater, or brine.

Traditional vs. High-Efficiency Systems: Older RO models can produce four or more gallons of wastewater per gallon of purified water. Newer systems with permeate pumps significantly improve these ratios, sometimes achieving 1:1 or better, though a waste stream is still inherent.
Impact on Water Bills: High water usage can lead to increased water bills.
Alternative Uses: Some users repurpose reject water for non-potable uses like gardening.

The Stripping of Essential Minerals

RO's ultra-fine membrane removes nearly all dissolved solids, including beneficial minerals like calcium and magnesium.

Health Implications: The WHO has raised concerns about long-term consumption of demineralized water and potential links to mineral deficiencies, especially in populations with poor diets. While most diets provide adequate minerals, water contributes, and reducing this source can be concerning over time.
Negative Impact on Taste: Mineral removal results in RO water having a 'flat' taste compared to mineralized water.
Remineralization Solutions: Some modern RO systems include a stage to add minerals back, improving taste and addressing health concerns.

The Issue of Acidity and Potential Corrosion

Removing minerals can lower water's pH, making it slightly acidic. While minimal health effects are debated, acidic water can be corrosive to plumbing, potentially leaching metals like copper into the water.

Performance and Maintenance Challenges

RO systems require more complex installation and ongoing maintenance.

Slow Production Rate: Filtering water through the membrane is slow, requiring a storage tank for on-demand use.
High Upkeep Costs: Initial costs are higher, and periodic replacement of filters and the membrane is necessary, adding to ongoing expenses. Neglecting maintenance can lead to system failure or poor water quality.

Comparison Table: Reverse Osmosis vs. Activated Carbon Filtration


Feature	Reverse Osmosis	Activated Carbon Filter
Removes Dissolved Solids (TDS)	Yes, highly effective (92-99%)	No, does not remove TDS
Removes Healthy Minerals	Yes	No
Effectiveness Against Contaminants	Wide range (lead, arsenic, salt, fluoride, PFAS, nitrates)	Good range (chlorine, chloramine, pesticides, VOCs)
Water Waste	Significant, though improving with newer models	None
Filtration Speed	Slow, requires storage tank for volume	Fast, immediate flow
Initial Cost	Higher	Lower
Maintenance Cost	Higher (multiple filters and membrane)	Lower (carbon filter replacement)
Installation	Complex, often requires professional help	Simple, DIY-friendly options
System Footprint	Larger (multiple filters + tank)	Smaller (single unit)

Addressing the Drawbacks with Modern RO Solutions

Modern RO technology has addressed some historical drawbacks. High-efficiency models reduce water waste, and remineralization filters restore beneficial minerals and improve taste. Tankless systems offer compactness and on-demand water. Consumers should research specific features to find systems that mitigate their concerns.

Conclusion: A Balanced Perspective on Reverse Osmosis

Reverse osmosis offers superior contaminant removal but has notable downsides like water waste, mineral stripping, and ongoing costs. Modern systems have addressed some issues with improved efficiency and remineralization options. For those prioritizing ultra-pure water despite the drawbacks, RO is effective. However, simpler carbon filtration may be suitable for those focused on chlorine removal and taste without the waste. Consider water testing and explore options like those detailed on the EPA's website before deciding.

Visit the EPA's website to learn more about water quality standards and consumer information

Frequently Asked Questions

For most individuals with a balanced diet, drinking RO water is not inherently bad. While it removes essential minerals, the majority of minerals are typically gained from food, not water. Health risks primarily concern individuals in areas with poor nutrition, but remineralization can counteract this.

RO water is often described as tasting flat or bland due to the removal of all dissolved solids, including minerals that contribute to water's flavor. Many modern systems include a remineralization stage specifically to restore a more pleasant taste.

Older RO systems can waste 4 or more gallons for every 1 gallon of purified water. Newer, high-efficiency models with permeate pumps can significantly reduce this ratio, often achieving 1:1 or less, making them more water-efficient.

Yes, by design, the semi-permeable membrane in all RO systems removes dissolved solids, including minerals. The difference lies in post-filtration options, with many newer systems including a stage to re-add healthy minerals.

Yes. When minerals that buffer pH are removed, the water can become slightly more acidic (lower pH). For most healthy people, this is not a concern, but it can contribute to plumbing corrosion over time.

The filtration process is slow by nature due to the ultra-fine membrane. Under-sink systems use a storage tank to ensure you have purified water available on demand, but the tank itself takes time to refill.

Alternatives include activated carbon filters, which remove contaminants like chlorine but leave beneficial minerals, or distillation systems, which also produce demineralized water but use a different process.