Reverse osmosis (RO) is one of the most effective water filtration methods, removing a wide range of contaminants from water. RO systems use a semi-permeable membrane with extremely tiny pores (about 0.0001 microns) to filter out particles, molecules, and ions. Here’s a breakdown of what reverse osmosis removes:
1. Dissolved Salts and Minerals
- Sodium, calcium, magnesium, potassium: Common in hard water and dissolved salts that contribute to water’s hardness.
- Effectiveness: RO removes 95-99% of dissolved salts and minerals, making the water “soft” and improving its taste.
2. Heavy Metals
- Lead, arsenic, mercury, chromium, copper: Harmful to human health even in small quantities.
- Effectiveness: RO can remove up to 99% of heavy metals, making the water safer for drinking.
3. Chlorine and Chloramine
- Chlorine and chloramine: Added to municipal water supplies for disinfection but can leave a chemical taste.
- Effectiveness: RO systems with pre-filters (like carbon filters) effectively reduce or eliminate these chemicals, improving taste and smell.
4. Fluoride
- Fluoride: Commonly added to water for dental health but is often a concern for some consumers.
- Effectiveness: RO removes about 95-97% of fluoride from water.
5. Pesticides and Herbicides
- Glyphosate, atrazine, DDT: Common agricultural chemicals that can seep into groundwater.
- Effectiveness: RO membranes effectively remove pesticides, herbicides, and similar organic contaminants.
6. Pharmaceuticals and Hormones
- Prescription drugs, antibiotics, hormones: These trace contaminants are becoming more common in water supplies.
- Effectiveness: RO can remove these substances, though it is more effective when paired with carbon filtration.
7. Bacteria and Viruses
- E. coli, Salmonella, Giardia, Cryptosporidium: Harmful microorganisms that can cause illness.
- Effectiveness: RO removes bacteria and viruses by blocking them at the membrane, which has pores small enough to prevent passage.
8. Nitrates and Nitrites
- Nitrates and nitrites: Often found in agricultural runoff, they are harmful, especially to infants.
- Effectiveness: RO removes up to 90% or more of these contaminants.
9. Total Dissolved Solids (TDS)
- Dissolved salts, organic compounds, and minerals: TDS includes various substances dissolved in water.
- Effectiveness: RO is highly effective at reducing TDS, resulting in water that is purer and free from unwanted dissolved substances.
What RO Does Not Remove (Completely):
- Some Volatile Organic Compounds (VOCs): While RO can reduce many VOCs, certain ones may require an additional carbon pre-filter for full removal.
- Certain gases: Because some gases (like radon and chlorine byproducts) are smaller than water molecules, RO may not fully remove them unless paired with a carbon filter.
How RO Works with Other Filtration Stages
Most reverse osmosis systems include multiple filtration stages to maximize contaminant removal. Typically, an RO system has:
- Sediment pre-filter: Removes dirt, rust, and large particles before water reaches the membrane.
- Carbon pre-filter: Reduces chlorine, chloramine, and organic chemicals that can damage the RO membrane.
- RO membrane: Removes dissolved salts, heavy metals, and many contaminants listed above.
- Post-carbon filter: Polishes the water, removing any residual tastes or odors for the final clean water output.
Final Thoughts
Reverse osmosis is one of the most comprehensive filtration methods available, removing up to 99% of a wide range of contaminants, including heavy metals, dissolved salts, bacteria, viruses, fluoride, nitrates, and more. While highly effective, it’s often paired with other filters like carbon filters to handle any compounds that may slip through. Regular maintenance of the system, including filter changes, ensures maximum effectiveness in producing clean, safe drinking water.