Sulfate in Water

A naturally occurring mineral salt dissolved from rock.

Sulfate is a mineral salt water picks up from gypsum and other natural deposits. At high levels it makes water taste bitter and — famously — has a laxative effect on people not used to it, which is why visitors sometimes react to well water the locals drink without a thought.

What it is

Sulfate is among the most common dissolved minerals in groundwater. It isn’t toxic in the usual sense — the concerns are taste, digestive comfort, and its tendency to corrode plumbing at very high concentrations.

How it gets into water

Water dissolves sulfate from gypsum, shale, and other rock as it moves underground. Industrial discharge and mine drainage add to it in some regions. Well water in arid areas tends to run highest.

What a result can tell you

The EPA’s secondary guideline is 250 mg/L — above that, most people notice bitterness, and unaccustomed drinkers (including infants and guests) may experience temporary digestive upset. Persistent high readings suggest checking whether reverse osmosis or distillation treatment makes sense, especially for households with young children.

What it can’t tell you

Sulfate level doesn’t indicate bacterial safety or metal contamination — water can be high in sulfate and otherwise excellent, or vice versa. If rotten-egg odor accompanies a high reading, that’s hydrogen sulfide’s doing, a related but separate marker on your strip.