Everything you could possibly want to know about how dishwashers work

If you’re lucky enough to have a dishwasher, you’ve probably given thanks for its time-saving nature. But have you ever wondered: How do dishwashers work? To build the best dishwashers, engineers from every appliance manufacturing company come up with slightly different ways to construct dishwashers, which means that even though they generally do the same thing, each looks and operates a little differently.

From spray arms and drying mechanisms to materials and control panels, there may be differences between brands, but they all have the same end goal: clean, dry dishes.

Read on for a breakdown of how dishwashers work.

The basic components of a dishwasher

The tub and door: Ensuring a watertight environment

The interior of a dishwasher is comprised of the tub and the door, which is sealed with a rubber gasket to ensure water doesn’t leak out during the washing process.

Dishwasher tubs are typically made of either plastic or stainless steel. The latter is better for noise-dampening, heat retention, and durability. Plastic can become brittle over time, so it may crack or stain more easily, especially in areas with hard water that leads to mineral buildup.

To create more affordable dishwashers, manufacturers make hybrid tubs with plastic portions and others, such as the door, that are stainless steel. This reduces costs and adds some of the benefits of stainless steel.

Control panel: User interface and selection of settings

Whether front-facing or positioned on the top of the dishwasher door, the control panel is an important consideration in purchasing a dishwasher. Some have actual buttons to push, while others are digital or touchscreen. Many also incorporate Wi-Fi and connect to an app for more controls and features.

Spray arms: The role of water pressure

You may not think a lot about the spray arms when considering your dishwasher, but they are the most important feature in ensuring clean dishes. The function of the spray arms determines if enough water, at a high enough pressure and the right angle, hits the dishes to get them clean. (More on this in the Spray arms and their functionality section, below.)

Filters: Keeping the wash water clean

There was a time when dishwashers had built-in garbage disposals, but the cost, complexity, and maintenance issues they caused made the combination undesirable. Dishwasher filtration systems have improved significantly so they can trap small food particles and keep them out of the wash water.

The filter is the dishwasher’s first line of defense against food residues, and keeping it clean prevents redeposit, which is when food particles are removed from one surface but land back on another. It’s typically located under a removable cover at the bottom of the dishwasher, and can easily be removed, then rinsed or scrubbed.

Be sure to locate the filter and get familiar with how it works before you toss your user manual. It is important to clean your dishwasher filter regularly to keep it properly maintained and functioning well. This also has an impact on long-term dishwasher performance and could help extend the life of your dishwasher.

Plumbing and heating elements: How dishwashers circulate and heat water

The inlet valve connects to the home water supply, and a pump inside the dishwasher housing is responsible for circulating and draining the water. Dishwashers need hot water to effectively clean dishes, so they employ a heating element and sensors to regulate water temperature.

Some dishwashers use the same heating element to create a warm environment to dry dishes as well, while other manufacturers use different drying methods that don’t involve a heat source, like zeolite.

Detergent dispenser: Powder, liquid, or pods

The detergent dispenser is typically located in the door of the dishwasher and automatically opens to release the detergent at the appropriate time in the wash cycle. There is also typically a port for rinse aid next to the detergent compartment. More on the importance of detergents and rinse aids, below.)

Dishwasher cycle phases

Dishwashers are programmed with several different cycles (Normal, Heavy, Sanitize, Auto, etc.), but they all have a similar set of phases that begin when you hit start.

1. Pre-Wash rinse: Removing loose food and debris

The first phase is a rinse phase, circulating hot water through the spray arms to ensure all the debris on the dishes is moistened and ready to be washed away.

This brings up the age-old (and often argued) question, should you rinse your dishes before putting them in the dishwasher? The definitive, and water-saving, answer is “No!” In most modern, well-functioning dishwashers, you don’t need to pre-rinse dishes as long as you give them a good scrape to remove large bits of food. We know, it’s a tough habit to break, but just give it a try!

2. Wash: Applying high-temperature water and detergent

After the initial rinse, the soap is dispensed, and the spray arms get to work circulating high-pressure water around the machine to effectively scrub everything inside with sudsy water. As the soapy water drains, the filter works to capture any debris and prevent redeposit.

3. Rinse: Removing detergent and food residues

This phase is pretty self-explanatory. Clean water is circulated through the machine to rinse away everything that shouldn’t be there, leaving clean dishes that are ready to be dried.

4. Dry: Methods of removing moisture from dishes

Once upon a time, dishwashers relied on a heating coil at the bottom to dry dishes, but to reduce energy consumption and improve safety, many manufacturers have eliminated this element in favor of fans or other technological advances. Modern dishwashers employ a variety of different methods for drying dishes, which can drastically impact performance and cost.

Some dishwashers use a built-in heater, usually in combination with a built-in fan, to circulate hot air to evaporate water. Others automate the door to open slightly after the final rinse cycle to let out moisture and encourage evaporation. Bosch (the brand we’ve found best at drying dishes) employs a system called CrystalDry, which uses a mineral called zeolite to enhance drying, and it works better than any other systems we’ve tested.

If your dishwasher isn’t particularly good at drying dishes, and it doesn’t have any of the automatic enhancements mentioned above, you can help the drying process by leaving the door slightly open as soon as the rinse cycle finishes.

Rinse aid also plays a role in helping to ensure dishes come out as dry as possible, so don’t skip adding it to your dishwasher. More on the importance of detergents and rinse aids, below.)

Which cycle should you choose? Spoiler: It’s auto!

There are a lot of cycle options on modern dishwashers. It may be tempting to avoid confusion and always just hit “Normal” unless you’re running a load with obvious needs like sanitizing or glassware only. But if your dishwasher has an Auto setting, that’s likely the best choice because the machine is equipped with a turbidity sensor (that’s a fancy scientific term for a sensor that can detect dirt and debris) that will adjust the settings according to what’s detected.

If your dishwasher has smart features, the Auto cycle may be called something like “Smart Wash” or “Sensor Wash,” but they all do essentially the same thing. Again, like avoiding pre-rinsing, it may seem risky at first, but the only way to find out how great it is is to give it a try.

Water heating and temperature

Hot water is key to clean, sanitized dishes. Food stains are more easily removed, and soap is more effective when mixed with hot water. While most sinks dispense water at a maximum temperature around 120°F, dishwashers use water between 130°F and 155°F, which means additional heating is required.

Dishwashers heat water using either a heating element located at the base of the tub or a flow-through heat pump to regulate the temperature needed for a cycle. When a cycle starts, water is pumped into the bottom of the dishwasher, where the heating element turns on, heating the water. Sensors determine when the water is at the correct temperature and then turn the heating element off.

The heated water is then pumped through the spray arms and onto the dirty dishes. Water is then filtered, reheated if necessary, and recirculated to wash the dishes. Some dishwashers have tech built in to adjust the temperature for the wash and rinse cycles, typically increasing the temperature for rinsing to promote evaporation and produce drier dishes at the end of the cycle.

Sanitizing cycles require a minimum water temperature of 150°F and often add time, as much as an hour and a half, to the wash or rinse cycle to achieve sanitization.

Detergents and rinse aids

Types of detergents and how they work

Although it wasn’t always the case, pods are currently the most popular form of dishwasher detergent. They’re also the most recommended by manufacturers and the most efficient. Just be sure to put the pod into the detergent dispenser to ensure that it is dispensed at the correct time in the wash cycle.

If you’re trying to save money, powder detergent is the recommended alternative because, like pods, it contains the two most effective cleaning agents—bleach and enzymes.

Gel detergents are less effective because they cannot contain both of these cleaning agents in a liquid solution. The bleach would kill the enzymes, therefore, gel detergents typically do not contain bleach and are less effective at removing tough stains like coffee and tea. Our own testing of dishwasher detergents confirmed all of this.

Scientific advancements in the enzymes present in dishwasher detergent have made it possible (and preferable) to skip pre-washing dishes before loading them into the dishwasher. Detergents use the power of food-digesting enzymes, which simulate the ones that live inside your digestive tracts and break down food for digestion and nutrient absorption. These enzymes require a warm environment, and research has led to enzymatic detergents that are effective at a wide range of temperatures.

Never put regular dish soap in a dishwasher, even if you’re in a pinch! The smaller bubbles it creates can damage the system or cause flooding.

The role of rinse aids in spotless dish drying

Even if you don’t understand how it works, you’ve likely seen the difference rinse aid makes in the final results of your dishes. Forget to use it and your dishes may come out wetter and covered in water spots.

Rinse aid contains chemicals called surfactants, which lower the surface tension of water so that it slides off dishes in sheets rather than beading up on the surface. This gets rid of water spots and speeds up drying by making the dishes hydrophobic. In other words, it prevents water on your dishes from pooling in droplets and instead forces it to run off in sheets.

Spray arms and their functionality

One of the most important aspects of dishwashers is the design and movement of the spray arms. The spray arms don’t just randomly circulate water around a dishwasher. They target pressurized water in specific directions based on the proper loading methods for that dishwasher. Manufacturers have devised the optimal ways to angle the pressurized water coming from the spray arms to attack the stains on dishes.

There is typically a spray arm at the base of the tub that’s primarily responsible for cleaning the bottom rack, and another spray arm in the middle that targets the upper rack. Some manufacturers have even begun to add dedicated spray arms for the third rack, which adds significant value to those dishwashers.

Loading methods in relation to the spray arm

Dishwasher racks may all seem the same at first glance, but the orientation and distribution of the rack tines vary from model to model and manufacturer to manufacturer. This is because each model is designed to be loaded a specific way for ideal cleaning. Pictures and descriptions of the ideal dish load are usually found in the user manual, and we recommend you keep it handy for the first several loads you run.

A combination of spray arm design and proper loading can greatly impact how clean your dishes get. Drastically deviating from the recommended loading configuration can prevent the spray arms from doing their job.

It's incredibly complicated to design a spray arm and rack configuration that can get all your dishes spotlessly clean, especially when you take into account the staggering number of possible dish and stain combinations. That's why there are so many different dishwasher interior designs.

The spray arms and placement of dirty dishes are vital to the proper operation of your dishwasher.

It’s important to understand your dishwasher manufacturer’s best practices for arranging dishes and utensils for optimal cleaning. For instance, many dishwashers now come with a third rack that can accommodate flatware, however, Miele dishwashers are specially designed to utilize the third rack for flatware and, therefore, don’t come with a silverware basket.

Many modern dishwashers, especially high-end dishwashers, have adjustable racks and foldable tines that can be rearranged to accommodate different configurations of dishware, cookware, and drinkware. Some of these dishwashers also come with smart features and Wi-Fi connectivity so that you can specify what’s in the dishwasher and how it needs to be cleaned.

If you’re investing in a smart dishwasher, it’s worthwhile to take the time to read up on the suggested loading methods and take full advantage of all the potential configurations and cycles your dishwasher offers. This will avoid damage, optimize your dishwasher’s capacity and efficiency, ultimately adding value to your purchase.

Dishwasher maintenance and cleaning

Because the main function of a dishwasher is cleaning, it may seem counterintuitive to realize that it doesn’t clean itself. Some dishwashers have a self-clean cycle, which is helpful, but if you’ve ever encountered a stinky dishwasher, even after a cycle is complete, you can probably recognize the signs that your dishwasher needs maintenance.

DIY maintenance: What you can handle and when to call a professional

There are a few easy steps to bring it back to peak performance. We already talked about the importance of regularly cleaning the filter, which will help keep odors and redeposit at bay.

There are also a few other regular cleaning tasks to keep your dishwasher in top condition, including deodorizing with baking soda and scrubbing the gasket where mildew and odors can build up.

While these minor maintenance tasks should keep your dishwasher running in top condition, there are a few issues that require a professional. If you notice standing water, incomplete cycles, or the dishwasher is not filling or draining properly. These issues could indicate problems like a malfunctioning pump, faulty spray arms, or a damaged control panel, which require professional diagnosis and repair.

A leak is also an important time to call a pro. Modern dishwashers are typically equipped with a leak-detection system that will stop the cycle if a leak is detected, but it’s best to get a plumber to diagnose and fix any potential leakage issues to avoid further damage. If your dishwasher doesn’t have a built-in leak-detection system, you can install a smart water leak detector near your dishwasher.

Our experts

Danielle DeSiato managed appliance coverage at Reviewed and has overseen testing of dozens of dishwashers. From evaluating the stand-out qualities of affordable dishwashers to the nuanced designs of third racks, she has spent hours considering all the attributes that make the dishwasher an MVP among home appliances. At home, however, she prefers to do the cooking and not the clean-up. Thankfully, her husband is a fantastic dishwasher and has a Bosch 800 Series dishwasher to help him out.