A toilet will normally use about 2-3 gallons per minute (gpm), a shower from 1.5 to 3.0 gpm, a bathroom or kitchen faucet from 2-3 gpm, a dishwasher from 2-4 gpm, and a washing machine from 3-5 gpm. When you start running more than one fixture (sink/dishwasher/toilet/etc.) at a time, the gallons per minute add up quickly. If you have a water softener or a special water treatment unit that restricts flow, you may see a pressure drop when several fixtures are operating at once.