There are a few strategies no one has pointed out yet, so I will venture.
1. Recruit Help
The average person is not an idiot, and will seek help for dangers they cannot realistically take on by their lonesome. What does this mean? Well, that any hostile waterbender looking to cause problems will likely end up facing another bender. I'd suggest having coldbenders, as they could effectively freeze a waterbender in their tracks (yes I made that dad joke and I regret nothing, it was glorious!).
Sure, a waterbender may have incredible supernatural abilities, which they can use at the speed of thought, but they're still human. Granted, that's a lot of power (and thus a lot of temptation), but most people aren't going to want to become outcasts or fugitives thanks to power abuse and will therefore avoid going down this path.
In other words, unless you're dealing with an absolute wacko, you can always try diplomacy. Chances are you and the waterbender can come to an understanding. If not, that's what #3 is for.
3. Sudden, decisive action
There's a quote from Mike Tyson. I don't know who he is, but I love how his quote applies to any magical world that exists or will ever exist. "Everyone has a plan until they get punched in the face." Waterbenders can react at the speed of thought, sure, but when you're caught off guard, your thoughts have a funny way of lagging behind the other guy's fist.
Shock (whether physical or mental) and confusion should logically render a bender incapable of wielding their power effectively or at all, thus giving ordinary citizens an advantage they can play as a last resort.
However, this also means guns, any weapon really, will be a potential issue, as most people don't expect to face a situation where someone has a weapon and intends to use it on them and go into shock when they end up in such a situation. I believe this will reduce the numbers of hostile waterbenders, as having incredible power is not necessarily going to reduce one's fear of death, sharp objects, or harmful projectiles.
4. Respect the bubble
Waterbenders have a relatively limited range of 1 meter around them, and other benders likely have the same range, so in a world of benders people will likely stay one meter away from all benders to compensate. If COVID-19 is any indication, this is perfectly feasible and relatively easy to put into practice.
Going off this, benders will likely be registered by the government, with severe consequences for those who evade this protective measure, so any waterbender who decides to abuse their power can expect a visit from their friendly neighborhood Anti-Bender Defense Force. Oh, and one other thing....
5. Hydro Extension
Studies have been done on the brain, and it's been found that violinist's brains change in such a way that the violin essentially becomes an extension of the body. A similar phenomenon will most likely occur for your waterbenders, causing them to feel the water around themselves as acutely as if it is part of them.
In other words, step in a puddle within a waterbender's range, and they'll feel an odd rippling sensation go through their body, causing them distinct discomfort. Think of it as the waterbender having a special receptivity to the water; they communicate with the water, sure, but they can only wield it because the water is giving them feedback, same as feedback from your body allows you to move it effectively.
However, this causes the waterbender to feel discomfort when water is disturbed around them, and may even cause them to feel overwhelmed when they have a lot of water around them (like when they are in a swimming pool). This is like you feeling your feet tingling when you try to wake them up (because when a waterbender is starting to use their power, they are 'waking up' to the water), or a young adult who had a quiet childhood getting sensory overload over entering the hustle and bustle of a big city.
This means that a waterbender has to get used to the discomfort caused by using their power, and can potentially lose focus (potentially even be stunned or knocked unconscious) when they go beyond a certain threshold. This threshold varies, but all waterbenders are stunned or knocked out upon their water being frozen, evaporated, or blown apart.
This also means that a waterbender can only have a certain amount of water around them, or they may pass out from sensory overload. This can be mitigated with enough training and experience, but it's still very possible for a waterbender to pass out in, say, the ocean, for its currents, waves, and various moving elements can easily cause overwhelming feedback.
Or in other words, since people are mostly water and waterbenders can bend blood, sweat, and tears, a waterbender could very well get overwhelmed in a crowd of people. With this, I believe the average citizen has a good chance against a waterbender.