Adding to the general confusion:
http://www.overclockers.com/articles609/
Methanol added to distilled water seems to do the trick. Not that I have tried it, but on the other side I didn´t write the article either.
Methanol at least is venomous/poisonous/toxic (my english isn´t good enough to sort these out) to keep You tubes free from algea, fungi etc.
regards
Mikael S.