The average dishwasher uses about 15 gallons of water per load. Various models range from 7.5 to 16 gallons per load. For comparison, a washing machine may use as much as 50 gallons per load of laundry washed. Any toilet manufactured since 1995 uses 1.6 gallons of water per flush while some older toilets used as much as 5 gallons per flush.
Improved efficiency dishwashers should use 7.5 gallons of water or less per load. Reaching this level of efficiency commonly requires replacing the existing dishwasher as there are no feasible modifications to existing machines to improve efficiency.
Saving Water with Old Dishwashers
Use water saver cycles, if possible, to reduce the amount of water used. Most importantly, only operate the dishwasher when full to capacity. This reduces the total amount of water used by reducing the number of times the dishwasher is operated.
Dishwashers Vs. Hand-Washing
Depending on the methods, hand-washing may be more efficient than running the dishwasher. Filling a sink with wash water commonly uses less than 7.5 gallons of water. If the dishes aren't rinsed under running water this can be a savings in the amount of water used. A running faucet can use up to 5 gallons of water per minute, although low-flow faucets reduce the water use to about 1.5 gallons per minute.