I always use distilled water for diluting film developer and the photo-flo final rinse. It's fairly cheap at about $.69 per gallon at discount stores.(posted 8369 days ago)The main reason for diluting Rodinal at 1:100 is not to save money, but to get the benefits of the higher dilution: more "compensating” effect (reduction in contrast), less grain due to reduction in developer alkalinity (Rodinal only), and higher acutance. Obviously, scenes (or films) which require more contrast would be more appropriately developed in Rodinal at lower dilutions such as 1:50 or 1:25.