1) your local water treatment plant is one good place to start....
(I run a 1 hour lab and have to watch these changes)
As each city has slightly different standards that each can handle
start there.
2) more importantly check with your sullpier of your chemistry.....
(In Canada there is a little bit of law called W.H.I.S., one of it's
little points os to list all chemicals used and how each is to be
handled.....right down to the film cleaner I use on the negs....)
/mark/