Glenn, I didn't see any "carbon filters no" advice, just a warning that if left to sit or overused, you can get a bacteria build up in them. The activated carbon is a receptor for bacteria, but also removes chlorine from water, that's why it's a must when used before resins and reverse osmosis units (chlorine will destroy the resin if concentrations are high enough and eat away at RO membranes), but also suggested to be followed up by another form of treatment (usually a fine filtration).

Nancy, I've built and maintained some of the ultrapure (18.2Megohm) systems for companies in the Seattle area. Those were always the fun ones, utmost care given to removal of bacteria...though most couldn't understand that UV radiation doesn't kill bacteria, just sterilizes them and that's why 0.2micron absolute filters must be used after them. Lots of fun going into clean rooms to work on systems as well, but Boeing had the best set up in one of their facilities...a fairly large room (about the size of a 4 car garage) dedicated to the system itself (prefiltration, RO, resin polisher beds, UV sterilization, ultrafilter system).

I know this has got a rats ass to do with dogs, but it is a fun diversion so I hope we don't get bumped.

Our systems are 18 megohm with a sand filter (if needed, softener (usually) carbon tank, prefilter, RO, UV, tandem mixed beds with dedicated tanks with certified resins, and 0.2 micron post filters and had a continually circulating loop. One site has acid injection before the RO. We had a dog of a time getting our water vendors to integrity test the post filters when they installed them; they kept arguing they were precertified and did not need it but you can have seating issues. I know pharma will integrity test on a regular schedule but we just do on install. We also don't integrity test the vent filter as it is an ambient system and we do not have the condensation issues a hot water system has.

Not as aggressive as pharma as this is REAGENT water and is way overkill. The deal is we release test results using the water in testing and want to take zero chances that the microbial testing comes back showing the water was out of spec. Some of these systems are five years old and have never had an OOS result. Pharm companies can test the water and put lot hold on products until the results come in, but we do not have that luxury.

Back to dogs. I let mine sit overnight as our municipal water is chlorinated and does not have chloramines and most of the chlorine will blow off. Other than that I really don't worry too much about animals who will eat horse poo and always have a mouth full of dirt after playing ball. If we are out and about they just get tap water.

I do use a carbon filter but my main point is a poorly maintained home system can do more harm than good and I would flush some water through a carbon filter if I was using it ambient. Mine goes right into the fridge. A lot of water quality is where you live.