The water here in Highworth comes out the taps in lumps!!The water in Swindon is very hard. It runs off the chalk hills. This article will explain. In fact it suggests it’s the hardest water in the country.
http://www.purewaterpeople.co.uk/blog/2014/06/hard-water-areas-in-england/
For the sake of £5 of distilled water there’s no point risking it round here.
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. The kettle even under heavy use is usually a single composite material, only gets to a high temp for several seconds then switches off. Now you think about your beloved 2.8 engine, many components, plastic, rubber various metals, then think about the hours you hoon around places like the peaks, temps going up and down all day but staying as a average high for sometimes hours. As you don't know whats actually in DRINKING water to make it safe for consumption, its possible those additives, given time are creating havoc on a consistently hot, pressurised, hostile environment?