I live in the UK, in quite a hardwater area, my shower head ( not in a bong, normal shower
) keeps clogging, and my kettle needs replacing every few months.
Having said that, I've been running with tapwater and antifreeze fine for ages. I use an aluminium heatercore and all copper blocks and fittings, and even when I pull my blocks apart, there isn't much evidence of problems.
There is normally a slight white residue on some areas of the block, but nothing major.
I'd recommend using distilled water and waterwetter, but my setup requires such large amounts of water, its simply not feasible. ( I have a radbox a very long way away from my PC, and I normally need a good 12-15 litres to fill the system. I'm not spending £10 on distilled water every time I need to change or test a block. )
my 2p anyway.