Does Reverse Osmosis Remove Heavy Metals from Water?

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Reverse osmosis can effectively eliminate heavy metals from water. This water treatment method can remove up to 99.1% of these metals from your drinking water.

So, what exactly are heavy metals?

Heavy metals are metals of relatively high density or with high relative atomic weight. They include mercury, arsenic, chromium, thallium, manganese, cadmium, molybdenum, nickel, and selenium.

Drinking water that is highly contaminated with heavy metals can cause several health complications, like difficulty breathing, high blood pressure, and changes in vision.

How Do Heavy Metals Get Into Your Drinking Water?

Although some heavy metals might be naturally present in the soil, agricultural, industrial, and pharmaceutical processes are the major contributors to groundwater contamination.                        

Heavy metal-laden waste from mining areas, foundries, and smelting plants can also get into water sources. These toxic metals can also come from lead water pipes from old properties.

How Does Reverse Osmosis Remove Heavy Metals from Water?

Reverse osmosis water filtration works by allowing water molecules to pass through and rejecting larger contaminants molecules.

Generally, reverse osmosis systems filter water in multiple stages. The sediment-pre-filter removes sediment and large particles, while the activated carbon filter removes organic compounds and chlorine.

The activated carbon filter also reduces heavy metals like lead, copper, cadmium, and nickel from the water.

Next, reverse osmosis technology uses high pressure to push the water through a semi-permeable membrane.

The membrane has tiny pores that block heavy metals with larger molecules than 0.0001 microns from passing through. Only water molecules get free passage.

The heavy metals are then washed down the drain with wastewater.

Why Remove Heavy Metals from Your Drinking Water?

Heavy metals have serious health effects on humans, whether in organic or inorganic forms. The effects accumulate through long-term exposure to these contaminants.

Heavy metals can cause some of the following health problems:

  • Lead

High levels of lead can cause convulsions, coma, or death. It can also affect unborn children, damage the brain and injure other soft organs and tissues.

Lead can also result in kidney failure.

  • Mercury

Mercury can have toxic effects on the digestive and immune systems, on the skin, lungs, kidneys, and eyes. It is also a threat to the development of a baby in the uterus and early life.

  • Arsenic

Long-term exposure to arsenic from your drinking water increases the risk of cancer and skin lesions. The contaminant has also been associated with diabetes and cardiovascular diseases.

Exposure to arsenic in kids has been linked to poor cognitive development.

  • Cadmium

Exposure to cadmium in drinking water can cause fragile bones and kidney disease.

  • Chromium

High levels of chromium can cause damage to the liver and reproductive systems. It can also cause occasional irregular heartbeats, mood changes, sleep disturbances, headaches, and allergic reactions.

Is Reverse Osmosis the Only Option for Removing Heavy Metals from Water?

You can also remove heavy metals from water through ion exchange and chemical precipitation.

  • Ion exchange

Ion exchange method can reduce lead, nickel, mercury, cadmium, chromium, and copper in your drinking water. Heavy metal ions are attracted to the surface when water passes through an ion exchange resin bed.

Here, the metal ions easily swap places with safer ions like chloride. This makes the discharged water safe for cooking and drinking.

However, ion exchange has a few drawbacks, just like other technologies. For instance, it requires a thorough resin cleaning to work effectively.

This method can also filter essential minerals like calcium and magnesium from our water.

  • Chemical precipitation

Chemical precipitation is also widely used to remove heavy metals from drinking water.

Contaminated water is usually mixed with a chemical solution (containing lime) that reacts with the heavy metal ions. As a result, the metal ions precipitate into solids.

The precipitate is large enough to filter out with ease.

What are the Disadvantages of Using RO to Remove Heavy Metals from Water?

Although reverse osmosis is very effective at removing heavy metals from water, it has a few drawbacks:

  • It wastes a lot of water

When you filter water through reverse osmosis, some will go down the drain. The way RO water systems work is that water contaminants that cannot pass through the semi-permeable membrane accumulate in the RO membrane.

Unlike other water filtration methods, there is nothing for the pollutants to stick onto. The only solution is sending them down the drain.

  • Removes essential minerals

Reverse osmosis removes essential minerals like calcium and magnesium when eliminating contaminants from water. You have to add the minerals back to your purified water through remineralization.

  • Expensive

RO systems come with a high upfront cost. Expect to pay between $150 and $500 for a good unit.

  • Requires regular maintenance

For an RO system to remain effective, you have to exercise regular maintenance. You have to change the filters every 6 to 12 months and the RO membrane every 2 to 3 years for optimal performance.

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Dr. Peter Gleick

Dr. Peter Gleick is an experienced water filtration engineer and technical writer for He is an expert in water purification and filtration, focusing on helping people get clean, safe, and healthy water for domestic use. He has more than 10 years of writing experience and has numerously contributed to leading publications in this field.

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