Calcium Hardness Testing

Although there are strict standards in place for drinking water quality, the calcium hardness levels of water varies massively between areas. Drinking water with high calcium hardness is not known to have any adverse health effects. In fact, there are health benefits associated with hard water, as both calcium and magnesium are important dietary requirements. Calcium also improves the taste of the water.

When hard water is heated, dried or evaporated, the dissolved minerals are deposited, and limescale will form on taps and appliances, such as kettles. Hard water can also cause mineral build-up in your pipes and eventually clog them. Water companies do not soften water artificially at their treatment plants, but they will be aware of local water hardness.

The WHO state that public acceptability of the hardness of water may vary considerably between areas. They specify a taste threshold of calcium ions in the range of 100–300 mg/L. They also specify that water with a hardness above approximately 200 mg/L may cause scale deposition, but these are just guidelines rather than regulations or set limits.

The US EPA set out aesthetic guidelines; in the USA if water hardness exceeds 150 mg/L treatment is generally considered to prevent scaling.

Calcium hardness is important for swimming pools and spas to maintain healthy and pleasant bathing conditions. The baseline level of calcium hardness in pools and spas, will depend on the mains water supply used to fill the pool. This can then be affected by other parameters including temperature, pH and disinfectant levels.

If calcium levels are too low the inside walls of your pool or spa walls can be eroded by the water. Likewise, if there is too much calcium, deposits will start dropping (as in a kettle) and can leave ‘hard water’ marks. To reduce the hardness of water in pools and spas, water can be diluted with mains water.

Calcium hardness should be measured once a week. In the UK, PWTAG state a level between 80–200 mg/L should be maintained. PWTAG is a UK-based, independent, non-commercia organisation, dedicated to raising standards in pool water treatment. Find out more about them here.

For more information on key test parameters for expert pool and spa management, download our helpful pool chemistry guide.

Hardness is an important water quality parameter that must be controlled to create the best environment for fish to grow. Calcium is important in the formation of bones and teeth, and in other biological processes.

High levels of calcium in the surrounding water will prevent the fish from losing sodium and potassium from their bodies. These two ions are essential to normal heart, nerve, and muscle function. Regular monitoring of calcium hardness will create a more conducive environment for fish to grow.

For more information about the key test parameters in aquaculture take a look at our case study on Water Testing at London Zoo.