Ride down the ramp and defeat the enemies. Stand in between the water cascades, freeze time and bounce off of them to get to the upper level.
Use the wall and go round the room. Jump onto the waterspout, then onto another and go to the second part of the sewer.
You will encounter the sand beasts summoning enemy for the first time. Don't approach him without hitting immediately, as he will knock you off and the Prince will lose some health. In order to get as many experience points as possible, kill the beasts he summons until the green orbs stop appearing. Afterwards kill the summoner. If, on the other hand, you want to finish the fight as fast as possible, get rid of the summoner firstly and then take care of the beasts. After the fight, get to the crank by jumping off the walls.
Turn it twice to activate the water streams. Use them to reach the lever which will raise the bars.
Return to the crank and turn it so that waterspouts begin falling down from the ceiling. Use them to get to the further part of the sewer. Use the stones in the corridor and move on deeper.
Jump onto the higher level, run up the door and jump onto the lever. This will cause water to start falling down from the ceiling. Jump down and use the columns to get to the crank's level.
Turn it so that the columns change positions. Get back to the level from which you jumped on the lever a moment ago and use the columns to get to the next part of the sewer. Find the crated passage and use the wall to get onto the upper level.
Freeze time, run across the water and as you're to jump, let go off the freeze button so that the Prince can get through the cascade and onto the ledge. Afterwards freeze time again and get higher bouncing off of walls and water.