Your guide to dealing with a rogue Waterbender for the Average Citizen
The answer really depends heavily on the specific conflict, as the average joe is not going to beat a water bender if they are near a massive source of water (Like a lake or river), and even in their own homes the pipes could be dangerous if the waterbender can bend the pipes by bending the water inside them.
Even if a Waterbender has to touch them to bend the water inside, that's not to say the Waterbender can't drown them by effectively pouring water straight down into their lungs.
Really, the best tactic is to stay the hell away from a water bender
Assuming the average joe has ambushed said Water bender, all they'd need to do is stab them with a knife, or hell even take an axe to their neck. Not much a Water bender can do once you've buried a good inch of steel on em'.
Or if you want a less violent option, nd if the Water Benders rely on hand motions to move the water, you could slap cuffs on them and effectively neutralize them.
The average citizen would want to stay away from the range of a Waterbender, as this is would be the "kill zone" for the Waterbender. If the citizen has a gun (or hell even a nail gun, they can be quite nasty with a bit of modification) they could attack the water bender from a distance.
You don't really want to get near a Waterbender, since it seems they can control water at the speed of thought, which could be extremely bad. That is just game over. You could bull rush a Waterbender with a long weapon (like a hot poker or some kind of spear) and catch them off guard, but this could backfire horribly if they are ready for you or react fast enough.
Measures to take against Water Benders for a Society
Likely, a society with water benders would imprison naughty water benders within prisons that account for their water-bending properties, perhaps prisons where the cells don't have pipes with running water, or prisons deep underground away from any sources of water. You could put the prison in a desert, but I'm not sure of the legal ramifications or logistics of exporting water-bending criminals to foreign countries with deserts (for countries that don't have deserts). I have no idea how they'd keep said Water Benders hydrated without giving them access to potentially lethal water, however. ( Maybe their powers rely on hand-motions, so their hands are restrained in a way they can't make those hand motions? The threat of death, perhaps in the form of A Panopticon-style prison with a machine gun nest right in the middle?)
Police and other Authorities dealing with Water Benders would likely wear full body suits (something akin to Riot gear) to prevent Waterbenders from touching them and bending the water inside of them. Perhaps they'd also wear bulky breathing cannisters to prevent Waterbenders from trying to drown them via pouring water down their throat and nostrils.
I imagine Water Benders would also be registered in some government database, so that when police arrive in an area they'd be able to know if they'd be dealing with water benders.