Where's my Water! is a physics based puzzle game where you have to move water from one point to a drain connected to the shower of an alligator. It's a fun little game that progressively adds new mechanics and concepts and piles on replayability by having you collect things and fill ducks with water as well. I had a good time with it and I suppose it could be considered as a classic of sorts, resembling in spots with many other puzzle games.
There isn't much to say about WMW since it's all-around very good and charming. The puzzles aren't too difficult at first - although it's not obvious what you have to do in later maps. Some issue I had with WMW that I have with many others physics-based puzzlers is the unpredictability of it all. Even if you have an idea of what you need to do, you might fail because of some part in the simulation of physics that didn't act the way you thought it would. Luckily for such game you easily can retry and the levels aren't too long.
The only control you have in WMW is to break down dirt so liquids flow through. There is of course the already mentioned water, but after a while, other noxious liquids get mixed in and you need to avoid them - or use them at your advantage - to burn down plants for instance, all in the interests of getting water to your gator. Finding hidden items is as easy as breaking down all the dirt in a level and while the three ducks can be a challenge to fill, it's possible to complete a level and get them all, so you'll know if you're playing wrong.
There is a huge stage selection in the base game and you can probably buy many times as more as DLC and they all feel like a progression through more complicated systems. The only thing I disliked are levels with scrollbars to the left that you have to use because the level is too high to fit in one screen. They were unfun to use because they were not as responsive as you wanted and they sometimes appeared close to ground you had to break. Maybe making them bigger and more opaque would've helped.
If you've got time to kill and love physics puzzle, WMW is a pretty good one.