Water Hardness

All of the water we supply is classed as either hard or very hard. Water hardness is a natural feature and is a result of the geology of the area, being primarily limestone.  Minerals such as calcium and magnesium dissolve into the water as it moves over and through the ground. The level of these minerals in the water determines the water hardness. The information in the table below provides a general rule for classifying water hardness.

  Hardness description Total Hardness
mg/l Calcium carbonate UK Degrees Clark (°C) French Degrees (°f) German   Degrees (°dH)
Soft < 150 < 11 < 15 < 9
Hard 150 – 300 11 – 21 15 – 30 9 – 18
Very Hard > 300 > 21 > 30 > 18

mg/l = milligrammes per litre = parts per million = ppm

This information can be helpful when setting up household appliances such as washing machines and dishwashers.You can find out the hardness of your water supply using our postcode search facility.

Hard water in the home

Water hardness is not harmful to health and does not indicate a deterioration in the quality of your water supply. There are currently no maximum or minimum regulatory limits for water hardness.

Hard water can lead to the formation of limescale in both cold and hot water systems and increase the amount of detergent or soap used. Limescale will also form in domestic appliances that heat the water such as kettles and irons. Some of the limescale will stick to the surfaces of the appliance and some will remain as tiny particles in the water. Plastic kettles in particular do not collect limescale around the element.  When the water is boiled the tiny particles of limescale float freely in the water.These particles can react with the natural products in tea and coffee to form a film on hot drinks. This effect can be reduced by regularly rinsing your kettle.

In traditional hot water systems limescale can build up in hot water cylinders which can reduce their efficiency.   Combi boilers and electric showers heat the water directly.  Although limescale can build up on the heating element in these units a proportion of the limescale will remain as tiny particles in the water. These can sometimes aggravate existing skin conditions such as eczema.  Lowering the temperature of your hot water to 60°C can reduce the amount of limescale formed.

In the Bristol Water area we recommend you discuss water hardness with the supplier or installer first, as they may require a water conditioner or softener to be fitted before the unit.  Some customers also install a water conditioner or softener because they do not want the effects of hard water. There are a number of devices available that condition or soften the water and although we do not recommend a specific brand of water conditioner or softener, you may find the following general information helpful.