OK so I've knocked up a filter. It's just a used landcruiser diesel filter with a new 5um cartridge. I've hooked it up and the water coming out looks ultra clean - filled a glass jar up and shook it up then looked through against the bright blue sky. I couldn't see any trace of dirt.

The only problem is it smells faintly of diesel. I cleaned the housing very well - first blew it out with compressed air many times, then rinsed with metho, blew again and repeated about 4 times. Then I ran hot water through it for a couple of minutes. But still the faint diesel smell. Will this effect any of the chemical reactions? I've always understood straight hydrocarbons to be fairly inert, but could someone else comment?