Sulfates in Drinking Water

Sep 22, 2018

Environmental Enlightenment #180

Sulfate is a naturally occurring compound consisting of calcium (Ca), magnesium (Mg) or sodium (Na) in combination with sulfur (S), and oxygen (O4) atoms; thus CaSO4, MgSO4 or Na2SO4.

Consumption of sulfate by humans has a laxative effect.

At high concentrations, sulfate also has a minor objectionable taste. The drinking water guideline for sulfate is 500 milligrams per liter (mg/L) (*). Sulfate (S04) occurs naturally in groundwater.

(*) One mg/L is approximately one drop of the substance in 10 gallons of water

How does sulfate get into the groundwater?

As water moves through soil and rock formations that contain sulfate minerals, some of the sulfate dissolves into the groundwater. Minerals that contain sulfate include magnesium sulfate (Epsom salt), sodium sulfate (Glauber’s salt), and calcium sulfate (gypsum).

Are there health risks for humans who drink water containing sulfate?

People unaccustomed to drinking water with elevated levels of sulfate can experience diarrhea and dehydration. Infants are often more sensitive to sulfate than adults. As a precaution, water with a sulfate level exceeding 400 mg/L should not be used in the preparation of infant formula. Older children and adults become accustomed to high sulfate levels after a few days.

Can sulfate harm animals?

Animals are also sensitive to high levels of sulfate. In young animals, high levels may be associated with severe, chronic diarrhea, and in a few instances, death. As with humans, animals tend to become accustomed to sulfate over time. Diluting water high in sulfate with water low in sulfate can help avoid problems of diarrhea and dehydration in young animals and animals not accustomed to drinking high sulfate water. The ratio of water high in sulfate to water low in sulfate can be gradually increased until the animals can tolerate the high sulfate water.

Can sulfate cause other problems?

If sulfate in water exceeds 250 mg/L, a bitter or medicinal taste may render the water unpleasant
to drink.

High sulfate levels may also corrode plumbing, particularly copper piping.

In areas with high sulfate levels, plumbing materials more resistant to corrosion, such as plastic pipe, are commonly used.

How can sulfate be removed from water?

Three types of treatment systems will remove sulfate from drinking water:

  • reverse osmosis,
  • distillation, or
  • ion exchange.

Water softeners, carbon filters, and sediment filters do not remove sulfate. Water softeners merely change magnesium or calcium sulfate into sodium sulfate, which is somewhat more laxative.

Reverse osmosis (RO) is a water treatment system that removes most dissolved substances, such as sulfate, from water by forcing the water through a cellophane-like plastic sheet.

It can typically remove between 93 and 99 percent of the sulfate in drinking water. A small counter top RO unit will produce about 3 gallons per day. Slightly larger units that are usually installed under the sink will produce 5 to 20 gallons per day. RO units typically produce only 1 gallon of water for every 4 to 10 gallons of water treated. The remaining water goes to waste.

Distillation is a water treatment system that boils water, then cools the steam until it condenses into a separate container. The dissolved substances, such as sulfate, are left behind in the boiling pot.

With proper operation, distillation units can remove nearly 100 percent of sulfate. Distillation units require about four hours to produce 1 gallon of water, so this type of treatment uses a considerable amount of energy in its operation.

Ion Exchange is the most common method of removing large quantities of sulfate from water for commercial, livestock, and public supplies, but is not commonly used for individual household water treatment. It is a process where one element or chemical is switched for another.

Many people are familiar with water softening, one common type of ion exchange system. Water softening works by passing “hard” water — water with calcium and magnesium — through a tank filled with a special resin saturated with sodium ions. The hardness minerals stick to the resin, and the sodium is dissolved in the water. Ion exchange systems for removal of sulfate work in a similar manner, but use a different type of resin. Sulfate ions in the water exchange places with other ions, usually chloride, which is on the resin. When the resin is full to capacity with sulfate, it must be “regenerated” with a salt solution.

Water softeners for removal of hardness do not remove sulfate, and sulfate removal systems do not remove hardness, although some commercial units contain both resins and can remove both hardness and sulfate.

If both a water softener and a sulfate removal system are used, the water softener is usually placed before the sulfate removal system.

Acknowledgment: Minnesota Department of Health, Division of Environmental Health


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