Knock on wood, but I haven't been sick once since I started working out.
I do bring my own towel, but I just use it to wipe the sweat off my face and to put behind my head, I don't use it to wipe down the equipment (well, if I've really been sweating all over something, I'll wipe it down, but the wiping down thing is not a standard practice at my gym).
The water at my gym is from the kind of water fountain you had at your grade school (you know, the kind where you stick your head in it and hope no ones been putting their mouth on the nozel), so I'm pretty sure it is just straight tap water. Which I would never ever drink under any other circumstance. (Tap water in no. CA, esp. where I live, is so hard you can practically see the minerals floating around in it--in fact, you absolutely can see them if you freeze it and let it melt again. I don't know what that stuff is but it can't be good for you.) But I'm too lazy to carry around a water bottle so I drink the tap water at the gym.
I do think I have a good immune system that I developed through years of business travel (you are exposed to a lot of stuff on planes). That first year I traveled, I was sick all the time. Earaches, stomach flu three times, pink eye, colds, flu, you name it. After that first year though, I hardly ever got sick. Stuff would go around the office and everyone else would be sick, but I would escape. Of course, that second year of travel was also around the time I quit smoking, so I'm sure that had something to do with it too.
I eat at least one sugar-free vitamin C lozenge per day (it's like candy, but good for you

), although I think that provides more of a pyschological benefit than anything else.
Finally, I avoid using any anti-bacterial products. They aren't effective (colds and flus are mostly caused by viruses, which aren't killed by antibiotics) and eventually you'll develop an immunity to them. Then when you really do need an antibiotic, it won't be as effective. I used to get a lot of UTIs, and I definitely had to keep moving to stronger and stronger antibiotics so I'm a freak about this.
- Barbara