If you are measuring your water flow rates, you already know how much water you use in the tub and kitchen. If not, you may want to find out. Many differences exist between tub and kitchen faucets, however, due to their design and function.
Kitchen Faucet Flow Rates
Kitchen faucets have a flow rate of about 2.2 gallons per minute due to the aerator installed on the end of the faucet. It restricts water flow to a minimum level to conserve water. This flow rate varies based on several factors, however, including your home's water pressure, which varies between household, so actual flow rates are not the same in every home.
Tub Flow Rates
Since a tub does not have an aerator, its flow rate is determined solely by your home's water pressure. The tub spout may have a restrictive device inside the mouth to limit flow rates, however. Standard tubs generally run in the range of 4 to 7 gallons per minute because a tub spout fills the bathtub and does not run continuously like a kitchen faucet. Limiting the gallon per minute flow rate on a tub only restricts how long the water takes to fill the bathtub. Shower heads do have low-flow features to reduce water consumption. The typical low-flow shower head uses 2.75 gallons per minute but increases the area of coverage with a wider shower stream.
Measuring Tub and Kitchen Flow Rates
To measure the flow rate of a kitchen faucet, take a gallon jug and place it under the kitchen spout. Turn the spout on, and start a stop watch. When the jug is full stop the watch, and divide the number of seconds by 60, which yields a gallon-per-minute usage rate. Typically about 30 seconds passes to fill the gallon jug, which is 2 gallons per minute.
The Change in Tub and Kitchen Flow Rates
The Environmental Protection Agency initiated a flow rate reduction decree in 1992. Prior to this year, kitchen faucets could dispense up to 4 gallons of water per minute while shower heads and tub faucets served up 5 gallons per minute or more. After 1992, all kitchen faucets utilized flow rate reduction aerators. If your faucet is older, it might have a higher flow rate. In that case, changing the faucet is one way to save water.