Join Date: Nov 2007
Location: Lutterworth, UK
Distilled or de-ionized water is best, but ordinary tap water more than good enough too.
Tap water these days is fairly free of undesirables. Using a 50:50 mix, you won't put more than 3 litres of water into the system anyway and in 3 litres there simply aren't enough inorganic deposits that would foul the cooling system. The likeness to a kettle or iron is plain wrong. In these, the limescale build up over time from litres and litres and litres of water.
The cooling system is a sealed system...if you need to top up regularly, then use distilled water or better, get the leak fixed.
RIP 147 1.6 Lusso