One of the objectives in chapter 8 is to turn all valves blocking the drain of poisonous/spoiled water. On this page of our guide to Darksiders Genesis, you will learn what you have to do to drain the water.
The first valve is behind the poisonous waterfall.
Huge pipes are behind it - thanks to them, you will find the valve faster.
The second valve is located near the upper part of the waterfall. To get to it, you need to jump in the place marked in the screenshot above.
A small stone shelf with a Summoning Stone is behind the poison water pipes. Go there and jump down to move on. Grab the points at the bottom to move to the next location.
You will probably see a window telling you that your character has died. Don't worry, your character will respawn on the other side of the location. There you can turn the third valve.
The fourth piece of the puzzle is behind the exploding wall. You need to break the wall to get to that valve. Place Bomb Growths on it and light it with the nearby bonfire.
After that, you just need to jump on the rock and turn the valve.