You need window cleaning equipment. Our window cleaner has a nifty setup in the back of his van;

Big water tank filled from his garden hose, small pump pushing it through two 'resin tanks' which are basically fibreglass tanks filled with the special ion exchange resin. This gives 100% pure water from the hose.

We bought one rather large resin tank and plumbed it into a big water butt using a ball cock from a toilet, stuck that behind our wash bay and plugged jet wash into bottom of that so we've always got a massive tank full of 100% pure water, also used a paper filter inline before the resin tank as it's fed straight from mains so it catches the dirt and crap that comes through so extends the life of the resin crystals.

Considering it's for drinking, you should see the crap it stops!

Water round here was at 200ppm of solids, which is considered hard water, around 100ppm is average/soft. The resin gives us between 0 and 5ppm as long as we keep on top of the changing.

Supplies from Wintecs.