The object of the game is to guide the water from the top of the screen into the collecting vessel at the bottom of the screen, you do this by guiding the water down the screen using blocks, pressure valves and filters.
Monsters appear as the levels progress. Some of these are harmless and generally get in the way but others are nasty and can kill you on contact. Another breed of monster will also fire at you, luckily you have your gun so you can zap them.
On later levels it's not just water that comes out of the pipes, but acid as well. This is dealt with in the same way but you must avoid contact with it. Other features which will appear throughout the game include remote control doors, dissolving blocks, and drip valves to name but a few.