Best Under Sink Water Heater

Best Under Sink Water Heater

Under-sink water heaters are a great way to enjoy instant hot water at your sink.

They are amazing at reducing water waste while waiting for water to heat.

An under-sink water heater is designed to fit in small spaces beneath the sink. This means they will typically have a limited storage capacity.

This guide will take you through what you need to know when buying an under-sink heater. We will also review the best under-sink heaters to make your decision easier.

About Under Sink Water Heater

An under-sink heating system can be a great way for households to enjoy fast hot water.

They can be connected directly to hot water supplies for quicker hot water. If the under-sink water heater is your only hot water supply, it can be attached to your cold supply.

Different types of hot water heater systems can be installed in kitchens. These include:

Tank Water Heater

Water filters with tanks can provide instant hot water. A tank water heater is a great option for those with high water demands. It allows consistent hot water use while the tank lasts.

They are also able to store hot water. This can then be used at a later time and gives the user instant access.

Tankless Water heaters

A tankless water heater offers hot water on demand. This tankless system doesn’t pre-heat and store water.

It is an energy-efficient way of enjoying hot water. In some cases, a tankless water heater can reduce energy use by between 30% and 50%.

Reduced energy needs help to reduce energy bills. It is also great for those trying to reduce their CO2 emissions.


A filtered under-sink water heater can provide high-quality hot water. This option makes it possible for homeowners to enjoy hot drinks from the tap.

Typically, hot beverages made with a hot water tap will not taste as they should. Using a filtered water system can change that.

Other Considerations

There will always be other considerations when shopping for kitchen appliances. Unique individual needs will impact the choices you make.

If you are in the market for an under-sink water heater, the following considerations should be made.


Investing in a tankless water heater is a great way to enjoy hot water on demand. They can also save space beneath your sink. This means you don’t have to sacrifice as much storage space.

Alternatively, you might opt for an under-sink water heater with a tank.

Water heaters with tanks can be great options for larger properties or businesses. Higher water demands can benefit from hot water storage.

Under-sink water heaters typically have tanks that range in size from 2.5 to 7 gallons.

A 2.5-gallon tank will provide enough hot water for two to three basins full. If your hot water demands exceed this, a larger tank will be required.


Under-sink water heaters will have a range of features depending on the brand and model you choose.

Smart displays, filtration, and safety features are found in high-quality water heaters.

This ensures your family or anyone that uses the heater can do so safely. Child locks are a popular safety feature.

Auto flushing systems help to keep the system clean. This will minimize the risk of bacterial growth. It also helps to improve the water’s taste.

Anyone comparing under-sink water heaters should consider the features. Looking at cost without considering the benefits of its features can be a mistake.

Energy Efficiency

Under-sink water heaters are an efficient way to enjoy hot water in your kitchen. Using the home’s hot water supply can mean you are heating and storing more water than is needed.

An under-sink water heater will improve energy efficiency significantly. Using a tankless water heater gives you instant hot water. It also means you aren’t heating water that won’t be used.

Even tank-style water heaters can help you make savings on energy bills. They allow you to enjoy a hot water temperature without heating an excess amount of water.

The hot water and flow rate make dishwashing easy. It can boost your dish wash detergent’s power and result in cleaner dishes.


Using an under-sink water heater with a filtration system offers many benefits.

Filtered instant hot water is great for making hot beverages. You will have peace of mind knowing the water you use is free from contaminants.

Best Under Sink Water Heater

Choosing an under-sink water heater might seem like a daunting task. Thankfully, we are on hand to provide you with expert advice.

The following Waterdrop under-sink water heater is our top pick. Keep reading to find out about its excellent performance and great features.

Waterdrop K6

The Waterdrop K6 under-sink water heater is a great option. It uses reverse osmosis filtration to provide hot, pure water.

The Waterdrop K6 is the first reverse osmosis system with heating capabilities.

The innovative design provides an excellent 600 GPD flow rate. Hot water temperatures of between 104℉ and 203℉ can be reached.

This makes it great for cooking, hot drinks, and household chores.

This state-of-the-art model boasts a smart faucet. The display appears with a touch to show users the condition of the filter and TDS level.

Temperature adjustment allows you to select the perfect temperature for individual tasks. You can even enjoy cold filtered water. This makes it a perfect addition to any family home.

The 5-stage filtration system provides a better taste and reduces potentially harmful contaminants.

The first level is PP Cotton which filters sediment, rust, and other large particles from the water.

The next filtration level uses Carbon Fiber. This can help to remove residual chlorine. It also absorbs odor and color, making the water clear and scentless.

The Reverse Osmosis membrane then helps to reduce a variety of impurities from the water. These include:

  • Chromium
  • Salts
  • Fluoride
  • PFAS
  • TDS

A further Carbon Block is then implemented to help with the water’s taste.

A final layer of PP Cotton is used to remove any other large particles that might have made their way through.

The system is also designed in a way that limescale can’t form. This makes cleaning and maintenance significantly easier.

People concerned with water waste will enjoy the efficient system. The 2:1 ratio of pure water against wastewater is better than many filtration systems.

The Automatic Flushing feature helps to provide fresh water and minimize the risk of bacteria.

When you compare the Waterdrop K6 system against alternatives, it is clearly the better option.

Traditional reverse osmosis systems are unable to provide hot water. They are an excellent option for drinking water purification. However, without heating capabilities, they aren’t comparable.

Traditional instant hot water dispensers are another option. These systems don’t offer reverse osmosis filtration. This greatly reduces the quality of water as it is unable to remove potentially harmful impurities.

An instant hot water dispenser will also come with an ordinary faucet. In comparison, the Waterdrop K6 has a smart faucet with touchscreen capabilities.

Safety features include a child lock. This is essential for families and guarantees your children’s safety.

What We Liked

There are lots to like about the K6 water heater. The ability to enjoy instant hot water at various temperatures is great. The easy-to-use faucet allows you to adjust temperatures.

Adjustable temperatures provide you with greater choice. You can choose whether you want cold, filtered drinking water or steaming hot water for cooking or drinks.

The safety features mean you won’t have to worry about kids accidentally accessing the hot water.

The high-quality filtration system provides pure water for drinking, cooking, and cleaning. The pioneering use of reverse osmosis filtration reduces pollutants. This helps to improve purification results.

What We Didn’t Like

Regular use for drinks and occasionally dishwashing will be fine. More intensive hot water needs might need a more powerful water heating system.

Overuse can result in filters having to be replaced more frequently. It should not be seen as a replacement for the main water heater in your home.

Competing Brands

Waterdrop is a reputable brand with a range of excellent products. If you are interested in under-sink water heaters to provide you with instant hot water, the K6 should be perfect for you.

Other brands offer water heaters as well. We have found that they lack a number of features that make the K6 stand out.

Some alternative water heater brands include the following;


InSinkErator is better known for its range of garbage disposal systems. They offer a selection of basic water heaters.

The selection does not offer many of the features found with the K6.

The InSinkErator water heater selection does not offer filtration. They also come with basic faucets without temperature control facilities.


Rheem is a brand associated with large water heating solutions for the home. Their selection of under-sink water heaters typically has large tanks.

This can be useful if you have high water demands. Unfortunately, it also means a lot of under-sink storage space is taken up.

The water heater selection by Rheem is also relatively basic. It lacks many of the features of the K6. This includes filtration and smart controls.


Bosch is a global brand with an extensive range of home appliances. Their water heater selection offers tankless and tank water heater solutions.

This ensures homes can enjoy instant hot water. They are not as advanced as Waterdrop options. They are typically basic models without many features that appear on the K6.

Why the Waterdrop K6 is a better choice

The Waterdrop K6 water heater is the best choice for those that want instant hot water. The extensive range of benefits that Waterdrop offers make it a clear winner.

Multi-Stage Reverse Osmosis

Multi-stage reverse osmosis means the instant hot water you receive will be pure and clean. You will also be able to enjoy cold filtered water from the system.

The multiple layers minimize the risk of contaminants making it through to the drinking water.

Strong Filter Life

Filters will typically last between 6 months and 1 year. This will depend on the water condition and your usage habits. The reverse osmosis membrane will usually last up to two years.

Easy Maintenance

The limescale-proof system is recognized as being a low-maintenance option. Its automatic flush system keeps the system clean. Even changing the filters is easy and should only take a few seconds.

Support and Warranty

All Waterdrop products come with a 1-year warranty to protect you against manufacturing faults. The 30-day money-back guarantee ensures you are happy with how the system works.

Quick and Straightforward Installation

Undersink water heater installation is relatively simple with Waterdrop. They provide an extensive installation guide to help you.

You may need to drill through your sink or worktop to place the faucet.

If you are inexperienced, professional installation for your hot water heater is advised.

The straightforward system and detailed instructions will ensure it is a simple job for them.


The K6 is an energy-efficient way for you to enjoy instant hot water. The high-quality filtration system guarantees pure water for your home.

You will be able to enjoy hot and cold water from this system. The smart faucet technology and digital display make it easy to adjust the temperature range and get all the information you need.

An on-demand hot water system for your kitchen sink can improve cooking and cleaning. From washing vegetables to cleaning stubborn stains, the K6 is perfect.

The sleek design easily fits below sinks. The tankless model won’t take up much storage space.

When it comes to hot water heater solutions, the K6 provides a wonderful performance.

It is a unique design that provides an excellent temperature range. Most water heaters don’t come close when it comes to the features that Waterdrop provides.

About the author

Carlisle Edwards (Sr. Writer, Water Filtration) writes our content on water filtration, reverse osmosis, and avoiding waterborne contamination. He has experience in water and food safety and conducts microbiology research. He’s WaterAudit’s resident sports fan, and loves cheering on his local LA Galaxy soccer team.