What's the absolute worst thing those fish could do? Brutally ripping off her leg and drowning her in the bucket notwithstanding
Sterilizing hysteria probably costs more lives than it saves when it goes to this level of crap. I somewhat doubt everyone uses boiling water when it's easier to abuse antibacterial fluids and make the critters immune over time
Sorry to get pedantic, but there's a definite risk here. It's perfectly possible to transmit nasties from this, more so if a person has open wounds. You're basically using the same water (+ fishes) to clean everyone's feet. Any water-borne bacteria would have a field day with this. Especially when you consider that people with rough skin are probably more likely to have split skin and the like. You could probably try and do something to minimise this risk (although you would be unable to sterilise the water completely), but they didn't seem to be doing anything.
Also, boiling is just one of the ways they can sterilise tools. In all honesty, it's probably impractical anyway (the tools would be too hot and not available for immediate use, which would be important), so I'm guessing they use something else anyway. I’ve seen UV light used on tools at the barber, so perhaps that’s how they do it?
I'm guessing you're referring to antiseptic agents like alcohol, but bacteria can't really develop immunity to them, in the way that they can to antibiotics. They're just completely toxic to bacteria. If bacteria were humans, antibiotics would be like forcing somebody to do complicated genius level maths or die. Antiseptic agents are like setting the person on fire, you can't really adapt to it.