Kodak recommends 5 to 6 water changes using their fixer and clear. They suggest 20-30 minutes at a flow rate that equals one complete change of water in five minutes. The Ilford method would probably suffice, but one could easily modify it for two more fill-agitate-dump cycles if one was being conservative, and still not waste much more than a liter or so of water.
BTW, I use Kodak developer and Ilford Rapid Fix, which is non-hardening, but the Kodak fixer is probably more economical, and perhaps the hardener would have prevented some ill-fated scratches I now deal with in older negatives. I don't know. But it can't hurt. The next time I buy fixer, it will be Kodak for the hardener, but that's probably superstition and hope more than logic. I just know how crestfallen I was finding a long scratch across a favorite shot when I pulled it from the sleeve. If hardener helps, I'll take it.
I now use only distilled water for the final rinse with a PhotoFlo-type product. Lessons learned the hard way 🙂 (or rather, 🙁 ) I do have a Brita filter, but filtered water is not distilled, and even though my water is soft (taken from a river but treated for city water supply) the filtered water left spots galore on my negatives. Distilled is cheap, available at gas stations for less than a buck a gallon, and totally resolved the spotting issue. For the price, I now can't see using anything else for the final rinse.
I'm not sure distilled is necessary for the other steps, but everyone's water is different. Nothing is more frustrating than having everything else turn out wonderful, but seeing huge globs of residue ruining an otherwise great shot. You can rinse again to clear the spots, but it's a pain when you can do it right the first time so easily.