Anyway, helmets, seatbelts, jaywalking, whatever, you shouldn't get imprisoned. You may get ticketed though. So, just like speeding, go ahead if you want to risk getting ticketed. There are speed limits for a reason too (although they should be raised). Here in Toronto, we recently made texting while driving against the law. Get caught, get a ticket. I don't see that as really preventing something. And as such, it isn't government control. More like encouraging or reinforcing safe behaviour. Don't follow if you want, but just know it isn't safe and you may get a ticket.
If you don't want such things to be something enforced, policed, or ticketed. That's fine too. Then the government should invest in educational campaigns instead. Not against the law to not use a seatbelt, but there may be commercials to encourage their use for instance. Knowledge is power XD
To use your water analogy though, I would see the equivalent to what I was proposing as the government providing clean water through your taps. Want to drink it? Go ahead. Want dirty water? Go to a lake. Want to buy water? You can do that too. Options. But, by the presence of the clean water they're encouraged to use it over lake water should they want a drink of water. Don't want to wear a helmet, okay. Go ahead. But through the presence of a law (even if it isn't enforced), you're encouraged to wear one. It's suggesting, not forcing. It's against the law here to drive without wearing a seat belt, but I'm not being forced to wear it. I can pull out of my driveway without it and likely no one will know. I have that freedom. But the threat or risk of a potential ticket encourages me to wear my seat belt (along with other better reasons).