Joe Scotto said:
Is a stop bath really necessary? I've heard that you can just use water.
Yes, it is true, water can be used. If you WANT a quick stop to the development action though, plain vinegar works pretty well. It is amply acidic to put the brakes on very,very quickly. Developing B&W 35mm film is really not even as difficult as setting up a Facebook account, to use a modern metaphor. Developing your own B&W film is actually kind of a fun, and fascinating endeavor. I think everybody deserves the chance to do it at least a few times. Shooting a roll of film, and then developing it is just...well, it's an experience like no other! Do not be afraid of it--it's really NOT that difficult!
Oddly, one of the more tricky things to source these days can be an affordable thermometer that will actually read the needed 68 degree temperature point. Mercury thermometers that can read the 68 to 70 degree zone are now difficult to find, and the flood of cheap, made in China health thermometers often do not go low enough. One solution is to keep your chemicals under the sink in the kitchen or bathroom, where the temperature is typically fairly constant, yet not too cold, and work at "room temperature", and keep good notes on the development times. I've done it that way for the past year, and I've read many different peoples' accounts of how they did it this way in "waterless darkrooms" that did not offer access to running water with temp control.
A "waterless darkroom" is where you pour chemicals into the developing tank, then single-use chemicals are poured out of the developing tank and out into a bucket, while re-usable stuff is poured back into a bottle, and one does the rinsing of the film by doing multiple water/agitate/let stand/dump out/repeat cycles. The rinsing or washing of film by that method is actually SUPER-efficient! Fill the developing tank with rinse water, agitate 10 seconds, let it just "stand" in the tank for 30 seconds,dump the water, and then repeat the agitation/stand/dump process multiple times. Do that for 7 minutes, you're golden.