The effects of limescale
If you live in the UK, there's a good chance that the water that comes out of your tap has got minerals dissolved in it. These minerals can deposit on surfaces and build up.
When it comes to electrical devices such as washing machines, this means that this limescale build up reduces the efficiency of your machine as it has to heat up the limescale before it can heat up the water. Limescale build up is a particular problem on the heating element. Over time, this limescale build up could render the machine inoperable. British Water say that a 1.6mm coating of limescale on a heating element can make it up to 12% less effective and making it more susceptible to burn out.
Different areas of the country can have varying degrees of water hardness and there can actually be large differences between towns that are geographically quite close, depending on the source of the mains water.
Water Softeners (aka Limescale Preventers)
Softening your water
Hard water interferes with some of the ingredients of the detergent, stopping it from performing at its best. The water in your washing machine therefore needs to be 'softened' to enable an effective wash of your clothes. A proportion of the detergent that you add to your wash is included to soften the water, before it gets about the job of tackling the dirt, grease and stains on your fabrics. If it's used to deal with water hardness, it can't then help with the cleaning.
There are a number of products which you can use in addition to your normal detergent which means that you can use less of it, which in most cases will save you money and help protect your machine from the effects of limescale.