Verdict: True. ENERGY STAR says a dishwasher uses about the same amount of energy and water regardless of how many dishes are inside, so running it half full uses roughly a full load's water for half the dishes.
Where the idea comes from
Washing machines taught people that a small load uses less water, since many washers sense the load and adjust the fill. It seems reasonable that a dishwasher would do the same. And in a small apartment or a household of one or two, waiting for a full rack can mean dishes sitting for a couple of days, which feels less hygienic than running it now.
What the evidence says
ENERGY STAR's dishwasher page says to "run full loads whenever possible," and explains that dishwashers use about the same energy and water regardless of how many dishes are inside. The same page warns that "rinsing dishes before loading increases the total amount of water and energy used," and suggests scraping food off instead. It also recommends the no-heat drying option and a rinse agent.
That makes the belief largely true. The water a dishwasher uses is set mostly by its cycle, not by the number of plates in the racks. Two half loads use close to twice the water of one full load.
In Southern California, where water use gets attention every dry year, that's a useful habit to get right.
What to do instead
- Load the dishwasher through the day and run it once it's full but not crammed. Every item still needs spray to reach it.
- Scrape plates into the trash or compost instead of rinsing them under the tap.
- If dishes will sit a day or two, scrape them well so food doesn't dry on.
- Use the no-heat or air-dry option when your dishwasher has one.
- Check your manual for a half-load or upper-rack-only option before assuming a small load uses less water.
Exceptions worth knowing
- •Some dishwashers have load options. A half-load or zone setting may adjust the cycle; how much it changes water use depends on the model, so the manual is the place to check.
- •Overloading isn't the answer. Nesting bowls and blocking the spray arms leads to rewashing, which uses more water than either choice.
- •Odor from waiting. If a partly full dishwasher starts to smell after a day, the filter or drain may need attention. See whether your dishwasher cleans its own filter.
- •Hand washing a few items is reasonable when the dishwasher would otherwise run nearly empty.
Sources
- •ENERGY STAR: Dishwashers (full loads; same water and energy regardless of load; scrape instead of rinse; no-heat dry)
The short version: Wait for a full, well-spaced load, and scrape instead of rinsing.
When a full, properly loaded dishwasher still leaves food behind, the spray arms, pump or filter may need attention. Call TrueFix Los Angeles at (213) 787-3989 or schedule dishwasher repair.