I never said you would cycle the water continuously. If the water isn't pure, I build an input cistern that then pumps (single pump, one way) into the "pure" one for hospital/bathing use. Sometimes i have to rely on stagnant pools or salt water, afterall.
Why would I even consider keeping a male buffalo that I can neither milk nor shear for seasons before getting one from the elves. What if the elves can't get one (biome restriction), or there aren't even any elves? Honestly holding onto your pack animals is a silly waste of resources. The grazers are too large (HUGE pasture sizes for a breeding population, if you can get one) and they are never shearable. So why breed bison and buffalo when I can breed more manageable sheep that double as textile production? Best thing to do with them is quickly butcher for a massive amount of "starter" food and some bones to make armor with (or xbow+bolts) or just to craft/decorate with for first caravan. Its about 30-50 food an animal depending on size. Even with using some tallow to ensure I start with soap, its more than enough food for your starter fortress (roughly a year's worth unless you get massive early migrant waves). You can focus more on setting up your fort than QUICK FARMS NAO! If you can't gather any berries/veggies to quickly brew and didn't bring something to brew/extra booze, I suppose you'll still need to plant a small patch though.
The main point of this is that the animals are just a burden. You -might- get a female milkable animal you can make a couple units of cheese from a year, but you'll have to pasture them above ground or pierce the caverns and pasture below. You can't breed them until you get more either, which usually means hoping your caravan (its from the same biome as you and brings animals) brings one of these AND its of the opposite sex. Then you wait for -years- trying to establish a breeding population from just two animals. This is waiting for paint to dry to gain sustainable food... by the time you can even get a proper breeding population out of the pack animals (5+ years with getting multiple animals from caravan) your fort is long established and mature enough to have long ago established enough farms, fisheries, hunting/trapping operations. Furthermore, they can't produce textiles. The only reason I put up with sheep (or lama/alpaca) is that they also produce textiles. Otherwise, you can use non-grazing birds (turkey) or even crocodiles to massively outstrip food production from other livestock with a fraction of the space. Pigs aren't grazers either. All that time and consideration to -maybe- benefit from the livestock long past when you need to anymore. It just isn't worth the 60-100 meat/fat+bones/leather you can instantly game to jumpstart the fort. I don't bring the oil/extra seeds to press either, because this would create even more work (build a screwpess and jugs at embark) and cost more points. The animals are one of the few free things you get. No matter what you do, you will always be forced to start with 2 random pack animals... which i see as food+bone+soap. Since I always start with -free- pack animals, and I always butcher them, then I always have tallow sitting there waiting to be used. So I bring cheap 2 point lye and make soap. So even if a dorf stubs his toe, I got soap at embark making sure it doesn't get infected.