The question has been asked and answered innumerable times, but we still do not have a definitive reply. There are valid arguments on both sides as to whether reverse osmosis (RO) water is good or bad for you.

Is Reverse Osmosis Water Good for You

We will address the topic from both angles and let you decide on the benefits or drawbacks of drinking RO water regularly, exclusively or not at all.

How Was Reverse Osmosis Discovered?

Looming water shortages in the aftermath of WWII caused then-Senator J.F. Kennedy to advocate the desalination of seawater.

In 1959, scientists at the University of California, Los Angeles (UCLA) developed a membrane that eliminated sodium chloride and dissolved solids from passing through it. This was precisely what was required for the large-scale process for desalination to be a success.

Reverse osmosis is used today for purifying water for commercial, industrial, scientific and residential usage.

What is Osmosis?

Osmosis is a naturally occurring process whereby a solvent e.g., water moves through a semipermeable membrane e.g., a living cell, from a lower concentrated solution to a higher concentrated solution, to the point where both concentrations are equal.

As defined by LibreTexts, “a concentrated solution is one that has a relatively large amount of dissolved solute. A dilute solution is one that has a relatively small amount of dissolved solute”. A solute is the dissolved substance, e.g., salt.

Reverse Osmosis – How Does it Work?

Reverse Osmosis is the exact opposite: it entails removing contaminants from water by forcing it under high pressure through a semipermeable membrane. The United States Environmental Protection Agency (EPA) broadly defines water contaminants as ‘anything other than water molecules’. The ‘other’ components are separated into four main groups: physical, chemical, biological, and radiological.

Reverse Osmosis

A semipermeable membrane allows the passage of some molecules, leaving the remainder to be discarded. Different strength RO membranes can treat three different types of water: tap, brackish and saline.

As making RO water requires only high water pressure, no electricity is needed. There is some waste, as you use more water to make the RO water than what you come out with, but there is minimal difference.

Is RO Water Acid or Alkaline?

Pure water (H2O) has a pH of 7, midway on the pH scale of 0-14, at 770 F (25o C).

A pH of less than 7 means the water is acidic, or soft. This can cause corrosion with the leaching of metals such as iron, copper, lead, zinc, and others. Alkaline water will taste metallic and acrid, as well as being potentially harmful.

‘Hard’ water has a pH of more than 8.5. It is not harmful, but its alkalinity may make it taste bitter. It may cause the formation of scale, which we often see on household items such as irons and kettles.

The pH of reverse osmosis water is between 6-6.5, making it more acidic than pure water.

Is Reverse Osmosis Water Safe to Drink?

Water in its natural state contains salts and minerals including bicarbonate, calcium, iron, magnesium, potassium, sodium and zinc. It also contains pyrogens (which induce a fever), bacteria and other microscopic organisms.

As RO removes about 99% of these substances, it makes the treated water potentially safe to drink. However, those salts and minerals are also vital building blocks for our bodies, and by not absorbing them in the recommended quantities, we could be doing more harm than good.

Electrolytes, comprising a solution of calcium, magnesium, potassium and salts, regulate the movement of water to cells and are vital to sustaining nerve impulses. The side-effects of too low an intake of the required minerals could result in general lassitude, muscle cramps, and in acute cases even heart disease.

RO water does not contain these electrolytes and is thus less hydrating than pure or alkaline water.

Nor does RO water contain antioxidants, as these would have been removed in the process of its conversion from pure water. Vitamins C and E along with minerals including copper, selenium and zinc combine to form antioxidants.

These can neutralize the effects of ‘free radicals’ – unstable molecules that contain oxygen but with an uneven number of electrons, allowing them to bond more easily with other molecules. This process can cause a chain reaction called oxidative stress, which can result in cell and tissue damage.

But RO water also has benefits in that the process removes other elements that put your health at risk, such as harmful bacteria, toxic chemicals and dissolved organic material. If imbibed, any of these substances are potentially fatal.

RO Water VS Distilled Water

Distilled water is water that has been purified, but not in the same manner as reverse osmosis.

Distilling means purifying or transform a liquid by successive evaporation and condensation. This is achieved by boiling it, then catching the resulting steam, and allowing that to cool and condense into another vessel. Essentially, you are transforming liquid into a vapor and back to liquid.

Distilling also removes contaminants such as minerals and salts from the water and can neutralize bacteria such as those that cause diarrhea and Legionnaires Disease, a type of pneumonia. Chemicals that have a similar boiling point to water may have to be treated with additional filtration to be removed effectively.

Where hard water can affect household items, distilled water is the better choice as it does not leave mineral deposits behind.

Both RO and distilled water may have a strange non-flavor, as the salts and minerals including sodium, magnesium and calcium that give it taste (salty, bitter and chalky respectively) have been removed.

RO Filters

Reverse osmosis filters come in various sizes, as well as micron values (one millionth of a meter) for filtering out different substances. These can range from .2 microns, getting progressively larger e.g., 0.5, 1,5, 10, 20 up to 50 microns. Each filter is used for a different substance, e.g., to reduce chloramine, chlorine, to fine sand, rust, bacteria, heavy metals, and herbicides amongst others.

Filters should be checked regularly to ensure they are still able to clean water effectively. The quality of the water that is being treated will affect the lifespan of the filters.

The best way to see if they need replacing is to look at them! If they look and feel slimy or slippery, it is time to replace the cartridge.

RO Water vs Bottled Water

We tend to reach for bottled water as we’ve been taught it is healthier than everyday water found in your home. However, this may not be the case. The water that comes out of your faucet may be equally healthy to bottled water, but more expensive. Bottled water is also much more costly than RO water in the long run.

Bottled water has many more disadvantages than cost: environmentally, it is much more dangerous. The plastic used to manufacture the bottles may contain the industrial chemical BPA. This can leach into the food or liquid that is contained in the can or bottle, causing harmful side effects to the brain, as well as potentially affecting children’s behavior. It may also affect blood pressure levels, fertility, and immune systems.

Plastic food containers are vulnerable to high heat environs, such as hot cars. It is better not to microwave any food in a plastic container, as the chemicals they contain may be transferred to your meal, especially meats and cheeses.

The FDA continues to monitor the usage of BPA and has determined that it is safe in low quantities.


There continues to be discussion and comparisons as to whether reverse osmosis, distilled or plain tap water is best. Many factors have to be taken into account, including cost, overall health benefits or hazards, green issues and not least, the taste of the product.

There are advantages and disadvantages to each, so in the end it will come down to personal preference.



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