Sprinkle on iOS, Android devices: fighting fires is fun:

There is something inherently fun that happens when water physics are done well. Take, for instance, Wave Race 64. The actual racing is only so-so, but when you add the rolling waves and sometimes choppy weather, you have a classic. Sprinkle is one of those great $1 apps for iOS and Android devices that may not last long, but the core mechanics are sound, and the splashing, streaming water effects are addictive. Splashing the water around the level and watching how well it's modeled is a large part of the fun here, and the act of putting out fires is weirdly calming.