In this post we explain why kettles get limescale, and whether limescale build up depends on the source of water. Before we do that, however, we will define hard water and soft water.
Hard water is water containing a relatively high level of dissolved minerals.
Soft water is water containing a relatively low level of dissolved minerals.
In England and Wales, most of the water treated and delivered to your tap is hard water. This is due to it being exposed to limestone, chalk, etc. There are however a few sources of soft water in the UK. Parts of Manchester which source its water from the Lake District enjoy the benefits of soft water as do the parts of Birmingham which take their water from the Elan Valley Reservoirs.
Limescale is a hard off-white substance which consists mostly of calcium carbonate and magnesium carbonate.
Limescale is caused by hard water. When it rains, the raindrops are composed of soft water. When this soft water soaks into the ground it absorbs various minerals (limestone, chalk, etc) and becomes hard water. Water treatment plants do not filter these minerals out as they are harmless, therefore these minerals end up coming out of your tap. Most of England has what is regarded as very hard water.
Limescale is a problem for two main reasons. Firstly it tastes gritty and makes your lovely cup of tea somewhat unpleasant. Secondly, limescale in large enough quantities can slow down, damage or even break your kettle (or whatever other machines/equipment that it forms in) .
Limescale is almost always found in kettles, but there are plenty of other places it likes to hide out. Pipes, particularly old ones, can get coated on the inside with limescale and therefore have restricted water flow. Washing machines and hot water boilers also gather limescale. In fact, surfaces of any kind can also acquire limescale.