Ensure that your hair is very clean and very dry. Any residue or moisture can interfere with obtaining the static electricity necessary for water bending.
Place the wide, shallow container directly under the water faucet that is turned off. This is to catch the water so that it won't go to waste. You can use it later for watering plants or washing dishes.
Put the cup inside the shallow container that is under the faucet. This will assist you in getting a smooth stream of water, and allow for adjusting the length of the stream.
Turn on the water faucet, and adjust the water flow until you have a smooth, steady stream with no breaks. This may get easier as the cup fills up, or if you elevate the cup with another container or dish.
Run the clean, dry comb through your clean, dry hair very quickly, combing the strands repeatedly to get the biggest static electricity charge that you can.
Bring the teeth of the comb slowly toward the water, holding the comb perpendicular to the stream. Make sure not to let the comb touch the water, but get as close as you can at about an inch beneath the faucet head.
Watch the stream of water bend as you move the comb.