What actually happens inside your dishwasher?

Understanding how a dishwasher works is key to learning how to get dishes clean.

Many people, according to the Internet, believe that dishwashers fill to the brim with water, making a swimming pool for dirty dishes. In reality, however, a dishwasher is closer to a car wash than a swimming pool.

Whether you’re trying to fix a misbehaving dishwasher or just curious, let’s take a closer look at what happens inside a dishwasher.

The importance of hot water

One of the key parts of clean, sanitized dishes is hot water. Water temperatures inside a dishwasher get as high as 130°F-140°F. The heating doesn’t happen instantaneously, however. The dishwasher pulls in water from your water supply via its external hookup.

When a cycle starts, water is pumped into a pool at the bottom of the dishwasher. The heating element at the bottom turns on, heating the water.

At the same time, the water in that pool is mixed with the detergent and sent into the spray arms found throughout the dishwasher, typically at the bottom and top of the dishwasher and occasionally beneath the top rack. The water surges through the spray arms, and hits the dirty dishes, hopefully taking some nasty food stains with it.

The dirty water eventually drips back into the pool below, where it is filtered, reheated, and sent back out into the spray arm again. The same water is being constantly used and reused, heated and reheated, sprayed and collected. See? It's much more like a carwash than a swimming pool (at least my swimming pool).

Once the water hits the desired temperature, the heater turns off, but the pumps continue pushing water through the spray arms. At the end of that portion of the wash cycle, all of the water is drained (that’s the gurgling sound you sometimes hear your dishwasher make), clean water takes its place, and the cycle begins anew.

So now that you know how a dishwasher works, we can dig into what actually happens during a modern dishwasher cycle.

A dishwasher’s cleaning cycle

1. Pre-wash/rinse

The first initial burst of warm water through the spray arm that gets all of the dirty dishes wet, but isn’t really aiming to do much cleaning.

Some dishwashers have a pre-wash detergent dispenser to add some additional cleaning power to this cycle, for when your dishes are really, really dirty. The pre-wash is typically only a few minutes long.

2. Main wash

Just what it sounds like: the main part of the wash cycle. The water is heated, sprayed, collected, filtered, heated, sprayed, etc., until the heating unit is turned off, while the spraying continues. At the end of the main wash, all of the water is drained.

Depending on the cycle, the main wash can take anywhere from 20 to 60 minutes, and may repeat multiple times throughout the cycle duration.

3. Final wash and rinse

This part pulls in new, clean water and begins the heating/spraying/filtering/heating cycle anew. Just like the main wash, the heater is eventually shut off while the spraying continues.

The final wash/rinse may or may not use detergent. Like the main wash, the final wash/rinse can take 20 to 60 minutes and may repeat multiple times throughout the cycle duration.

A graph of the temperature inside the dishwasher over time clearly illustrates the three main parts of a cycle:

There's one caveat worth mentioning here. Some dishwashers do not have built-in water heaters—they pull water directly from the source, so whatever temperature water happens to be circulating in the kitchen is the water that gets used to clean the dishes.

Washing with cold water may be the culprit behind unclean dishes or undissolved detergent pods. If this is the case, try running hot water at the kitchen sink (to purge the cold water from the system), then turn off the faucet once the dishwasher cycle starts. If the hot water at the kitchen sink stays on, it will pull hot water away from the dishwasher when it needs it most.

Depending on the manufacturer, additional rinses, heated drying to get your dishes dry, or other features may also happen, but pre-wash/rinse, main wash, and final wash/rinse are the core components of your dishwasher's cleaning cycle.

Other things to know about a dishwasher

Instead of a quick dip in the dirty water pool, it turns out your lasagna tray was repeatedly attacked by water-gunning spray arms loaded with hot detergent water. Significantly less relaxing, maybe, but much more effective at getting your dishes sparkling clean. Huzzah!

Even with the best dishwashers, there’s a chance that your dishes may not come out sparkling clean, but there are things you can do if your dishwasher isn’t cleaning dishes.

One thing to keep in mind: How you load your dishwasher is very important because dishes loaded in the wrong place could block a spray jet's access to other dishes.

Modern dishwashers are technological wonders that are extremely convenient and time-saving.

With judicious usage of spray arms and heated water, a dishwasher can clean your dishes much more efficiently than washing dishes by hand.