The distinct, unpleasant “rotten egg” smell in household water is the most common sign of a sulfur-related issue. This odor is caused by hydrogen sulfide (\(\text{H}_2\text{S}\)), which is a dissolved gas. Sulfur in water can also refer to dissolved mineral salts called sulfates, which are typically odorless and colorless. Determining whether the problem is the gas (\(\text{H}_2\text{S}\)) or the minerals (sulfates) is the first step in finding an effective treatment solution.
Boiling and Dissolved Gases
Boiling water can offer a temporary, point-of-use solution for removing hydrogen sulfide (\(\text{H}_2\text{S}\)) because this compound is a dissolved gas. The removal relies on volatilization, where the solubility of a gas in a liquid decreases significantly as the temperature rises. As water is heated toward its boiling point, the dissolved \(\text{H}_2\text{S}\) is forced out of the solution and escapes into the surrounding air.
This method primarily works for water containing very low concentrations of hydrogen sulfide, typically less than 0.3 parts per million (ppm). Boiling a small batch of drinking water can drive off the odor-causing gas, providing a momentary fix for consumption. However, this process requires proper ventilation, as the released \(\text{H}_2\text{S}\) gas should not be allowed to accumulate indoors.
Boiling is not a practical whole-house treatment because it only addresses the water being heated at that moment. The constant effort required to boil all household water, combined with the safety consideration of gas release, makes it unsustainable. If the \(\text{H}_2\text{S}\) level is high, boiling alone will be insufficient to fully remove the gas, leaving a noticeable odor behind.
The Limits of Boiling
In contrast to dissolved gases, boiling is ineffective against dissolved mineral compounds like sulfates. Sulfates are mineral salts, such as magnesium sulfate or sodium sulfate, that dissolve in water but do not vaporize with heat. Boiling water converts the liquid into steam, leaving all the non-volatile dissolved solids behind in the remaining liquid.
This process of evaporation concentrates the sulfate minerals, increasing their level in the water left in the pot. For example, if water containing 200 ppm of sulfate is boiled until half has evaporated, the remaining water will have a concentration of 400 ppm. Concentrations above 250 ppm can impart a bitter taste to the water.
Elevated sulfate levels can also have a laxative effect on humans and young animals, especially those not accustomed to the water source. Concentrating these minerals through boiling can contribute to the formation of scale or mineral deposits on cooking surfaces and appliances. Boiling water with high sulfate content is counterproductive and should be avoided.
Proven Methods for Sulfur Removal
Treating Hydrogen Sulfide (\(\text{H}_2\text{S}\)) Gas
Chemical oxidation is a common approach for treating the odor caused by hydrogen sulfide gas. This involves injecting an oxidizing agent, such as chlorine or hydrogen peroxide, into the water line. The chemical rapidly converts the \(\text{H}_2\text{S}\) gas into solid, odorless elemental sulfur particles, which are then removed by a sediment filter.
For lower concentrations of \(\text{H}_2\text{S}\), aeration is effective, which involves spraying or mixing air into the water to encourage the gas to escape. Catalytic carbon filters also work well for concentrations below 0.3 ppm by oxidizing the hydrogen sulfide into elemental sulfur on the carbon media surface. Whole-house manganese greensand filters can also be used, as they feature a coating that chemically oxidizes the \(\text{H}_2\text{S}\) into a filterable solid.
Treating Sulfate Minerals
Different technologies are necessary for removing dissolved sulfate minerals, which are not affected by oxidation or simple aeration. Reverse Osmosis (RO) systems are highly effective point-of-use treatments, forcing water through a semi-permeable membrane that rejects dissolved solids, including sulfates. Distillation is another point-of-use option that involves boiling the water and condensing the pure steam, leaving the sulfate minerals behind. For whole-house treatment of high sulfate levels, an ion exchange system is the most common solution, utilizing a specialized resin to swap sulfate ions for other harmless ions.