There are two forms of sulfur that are generally found in tap water: sulfate and hydrogen sulfide.

A combination of sulfur and oxygen, sulfates are a part of naturally occurring minerals in some soil and rock formations that contain groundwater. Over time, the minerals dissolve and sulfates are released into the water. Sulfates can be found in manmade hazards–such as landfills, pipelines, old septic systems, or industrial chemical factories. Sulfates do not produce an odor in water.

A colorless, flammable gas–hydrogen sulfide (of H2S) is most famed for its hallmark “rotten egg” smell. It can be formed as organic matter decomposes underground. However, the primary producers of hydrogen sulfide are sulfur-reducing bacteria. These bacteria, which use sulfur as an energy source, chemically change the natural sulfates in water into hydrogen sulfide. Sulfur-reducing bacteria thrive in oxygen-deficient environments (like landfills and deep wells) and can form in your water technologies (softeners, water heaters, etc). Subsequently, H2S (and the accompanying rotten-egg smell) are commonly described by people served by private or community wells.

Due to their different properties, sulfates and hydrogen sulfide make themselves known in water in different ways.

Taste: Sulfate minerals can cause scale to build up in your pipes. This may cause your water to taste bitter.

Smell: Sulfate does not produce an odor in water.

Stains: Increased sulfate levels, in combination with chlorine bleach, can make it challenging to clean your clothes. Sulfur-oxidizing bacteria can cause a blackening of water or a dark slime coating the inside of your toilet tank (similar to the staining effects of iron bacteria).

Taste: Elevated concentrations of hydrogen sulfide can impart a rotten egg taste to your water, It can also impact the taste and color of foods/beverages made with H2S-containing water (tea, coffee, etc.).

Smell: Hydrogen sulfide gas causes a distinct rotten egg smell. Most people are able to detect an H2S odor at a concentration as low as 0.5 parts per million (PPM). Heat volatilizes hydrogen sulfide. This means that warmer water temperatures increase the likelihood of the H2S moving into the surrounding air (and subsequently making it more easily detected by your nose). As such, it is common to notice the smell more strongly in your hot water, especially in the shower. Due to its volatile nature, it is also common that the smell dissipates after running the tap for a minute or two.

Stains: Hydrogen sulfide can corrode metals (like iron, copper, and brass) and may tarnish or discolor metal kitchenware. It may also cause yellow or black stains on your fixtures.

While it’s definitely a nuisance, this smell does not usually suggest any health risks at the concentrations found in your tap water.

The main concern with high concentrations (~500-1000 PPM) of sulfate in your drinking water is dehydration because sulfate can have a laxative effect. However, with time, those exposed to sulfate become acclimated and symptoms often disappear.

Water that smells like rotten eggs is usually not a health concern. While at high concentrations (>500 PPM) are dangerous (flammable and poisonous), most household H2S concentration falls below 10 PPM. At elevated concentrations, hydrogen sulfide in drinking water has been known to cause: nausea, illness, and (in very extreme cases) death.

The Environmental Protection Agency (EPA) has created two categories for drinking water standards. The first, the Primary Drinking Water Standards, are based on health considerations and are designed to protect people from toxic pollutants. The Primary Standards are legally enforceable thresholds. There are no Primary Standards for sulfate or hydrogen sulfide.

The other category–the Secondary Drinking Water Standards–are not legally enforceable. Secondary standards are based on taste, color, odor, corrosivity, foaming, and staining properties of water and are set to limit these nuisance effects.

Sulfate falls under the Secondary Drinking Water Standards category. The secondary maximum contaminant level (SMCL) for sulfate is 250 PPM–although only 3% of water supplies are estimated to have sulfate levels in excess of this level.

Hydrogen sulfide is not regulated under the Primary or Secondary Standards. A concentration high enough to be a drinking water health hazard also makes it unpalatable, and it is unlikely to be consumed. Generally, hydrogen sulfide levels in tap water are less than 10 PPM , but have been reported as high as 75 PPM.

While several methods are available for removing sulfate from your drinking water, the best choice depends on several factors including:

For treating small quantities of water, the most common methods are distillation or reverse osmosis (RO). For large quantities, the typical method is ion exchange.

In order to remove low levels of hydrogen sulfide that DO NOT include bacterial problems, the best solution is an activated carbon filter. Replace the filter periodically to maintain functionality.

For concentrations up to ~5 to 7 PPM, hydrogen sulfide can also be removed using an oxidizing filter. For higher concentrations, hydrogen sulfide can be removed by injecting an oxidizing chemical (i.e. household bleach or potassium permanganate) followed by filtration.