People with high blood pressure, diabetes and kidney failure can wind up with dangerously high levels of potassium in their bloodstream if they drink a lot of water filtered through potassium-based water softening devices.  Excessive blood potassium levels--or hyperkalemia--can lead to muscle weakness, irregular heartbeat and cardiac arrest.  People with hypertension, diabetes and kidney failure are at increased risk of hyperkalemia.  Recommended average daily dietary intake of potassium for a healthy adult is 2,700 mg to 3,500 mg.  Potassium works in a careful balance with sodium to control normal nerve function and muscle contraction, including a regular heartbeat, and to help balance the flow of water and nutrients in and out of cells.  Potassium plays an important role in controlling the balance of fluids in the body.

Acceptable results:  There is no health standard.  Best if under 20 ppm.

Sources:  Septic systems, road salt, fertilizers, animal waste, landfills or other waste, and erosion from natural deposits.

Recommended testing:  If in a risk area.  Annually for dairy cows if supplying water in dry and early fresh stages.