Classified as an alkaline metal and first identified by Sir Humphry Davy in 1807, sodium's name comes from the Latin 'natrium', meaning soda. Sodium is the sixth most abundant element in the Earth's crust and exists in many different forms such as minerals and salts, perhaps the most well-known salt being sodium chloride which is the chemical name for table salt. Salts of sodium are often very soluble, which gives rise to sodium and chlorine being the most common dissolved elements in the world's oceans by weight.
Sodium is highly reactive meaning that the free metal is not found in nature and can only be made from compounds that contain it. Besides as an edible salt, sodium chloride is also used to de-ice things like roads. Other sodium salts such as sodium hydroxide are used in the manufacture of soap.
Sodium is an important nutrient for both plants and humans with a certain amount of sodium being essential in the diet, helping to regulate blood pressure and pH. The minimum amount required by the body is roughly 500 mg per day for people over the age of 10, but many people have much more than this. The majority of the body's sodium intake comes from sodium chloride which is often used as seasoning, but sodium in drinking water may contribute about 10% to a person's total daily intake.
Despite the need for a certain amount of sodium in the diet, a higher than recommended intake is known to affect the function of the heart as well as being associated with chronic kidney disease, high blood pressure, other cardiovascular diseases, and strokes. The average daily intake for adults in the UK is 8.4 g, however the recommended amount sits at only 6 g.
Sodium in drinking water is very common and can come from several sources such as saltwater intrusion into freshwater, mineral deposits from rocks, seawater spray, and salt used in road de-icing. Some water treatment chemicals such as sodium fluoride, sodium bicarbonate, and sodium hypochlorite can increase the sodium content in water. Water softeners in domestic homes also exchange calcium and magnesium with sodium using resin beads.
Water regulations in the UK stipulate that tap water must contain less than 200 mg/L (ppm) of sodium, but the US Environmental Protection Agency (EPA) recommends that the concentration not exceed 30 to 60 mg/L to avoid adverse taste effects to the water.
Sodium in your drinking water can be detected by the following tests.
Sodium can be reduced or removed from your drinking water using the following methods.
