Sulfur is a naturally occurring element often found in water supplies, usually as either a dissolved mineral salt called sulfate or a dissolved gas known as hydrogen sulfide. While the presence of these compounds is generally not a health hazard at common household levels, they create noticeable aesthetic issues. The primary concern is the unpleasant odor and taste resulting from these sulfur-containing compounds.
The Chemical Forms of Sulfur in Water
Sulfur takes two main chemical forms when dissolved in water. The first is hydrogen sulfide, which exists as a dissolved gas. Because it is a gas, it easily escapes from the water when pressure changes, allowing it to be smelled.
The second primary form is sulfate, a dissolved mineral salt. Sulfate is odorless and does not cause the foul smell associated with sulfur water, but it is a dissolved solid. These structural differences mean each form causes different problems and requires entirely different removal methods.
Identifying the Presence of Sulfur
The most common indicator of sulfur contamination is a strong, distinct “rotten egg” odor. This smell is specifically caused by hydrogen sulfide gas and can be detected at concentrations as low as 0.5 parts per million (ppm). The odor often intensifies when hot water is used, such as in a shower, because heat forces the dissolved gas to escape more rapidly.
High levels of dissolved sulfate do not create an odor but can cause a metallic or bitter taste in the water. Hydrogen sulfide is also highly corrosive and can cause physical damage to plumbing and fixtures. This corrosion is often visible as black staining on silverware, copper, and brass fixtures, resulting from the hydrogen sulfide reacting with metals to form iron sulfide. While hydrogen sulfide levels are generally not a direct health risk, high concentrations of sulfate can have a laxative effect, particularly on infants and new users.
Sources of Sulfur Contamination
Contamination by sulfur compounds originates from two main mechanisms: natural geological processes and biological activity. Geologically, water moving through soil and rock layers dissolves naturally occurring sulfur-bearing minerals, such as gypsum or pyrite. This process releases sulfate into the groundwater, a common source of contamination in regions with shale, sandstone, or coal deposits.
The biological source involves sulfate-reducing bacteria (SRB). These anaerobic bacteria thrive in oxygen-deficient environments like deep wells, poorly circulated plumbing systems, or water heaters. SRB metabolize naturally occurring sulfate, releasing hydrogen sulfide gas as a metabolic byproduct. The magnesium anode rod found in many water heaters can also contribute to this problem by chemically reducing sulfate into hydrogen sulfide.
Home Water Treatment Options
The most effective home treatment method depends entirely on whether the primary contaminant is the dissolved gas (hydrogen sulfide) or the dissolved solid (sulfate).
Hydrogen Sulfide Removal
For removing hydrogen sulfide and its associated odor, several oxidation and filtration techniques are used.
- Aeration is a simple, chemical-free option where water is sprayed or mixed with air, allowing the dissolved gas to escape before the water enters the plumbing.
- Chemical oxidation is highly effective, often employing chlorine in a process called shock chlorination to destroy the sulfate-reducing bacteria.
- For continuous issues, a continuous feed of chlorine or other oxidizers like potassium permanganate or hydrogen peroxide can be injected. The oxidizer converts the hydrogen sulfide gas into elemental sulfur particles, which are then removed by a standard filter.
- Oxidizing filters, such as those containing manganese greensand or catalytic carbon, convert hydrogen sulfide into elemental sulfur particles upon contact. These particles are physically trapped and periodically flushed out during a backwash cycle.
- Activated carbon filters can be used, but they are only effective for very low concentrations of hydrogen sulfide.
Sulfate Removal
Treating high levels of dissolved sulfate is more difficult because it requires removing a dissolved salt rather than a gas. Sulfate is not effectively removed by simple oxidation or conventional filtration media.
For treating drinking and cooking water, a Reverse Osmosis (RO) system is highly effective, as the semi-permeable membrane rejects the sulfate ions. Distillation is another point-of-use option that removes sulfate by boiling the water and collecting the purified steam. For whole-house treatment of high sulfate concentrations, specialized ion exchange systems are employed, which swap the sulfate ions for a less objectionable ion, such as chloride.