Think of all the unconsumed foods, fish wastes, dead fish, debris, etc., in your aquarium. If you let these unwanted elements stay in your fish tank for long, they end up contaminating the water, making it uncomfortable and unhealthy for your fish.
However, an aquarium filter helps you easily remove all the physical and soluble waste inside your fish tank so that your fish can continue living in a cleaner and healthier environment.
In this post, we’ll talk about the most popular type of aquarium filter—the canister filter. We’ll take you through everything you need to know about this type of filter, plus our list of the 10 best aquarium canister filter currently available on the market.
What’s a Canister Filter?
A canister filter is an aquarium filter that helps removes undesired components from the aquarium water.
To do this, the filter takes water from your fish tank via an intake tube/valve/sieve and runs it through a filter media (in a pressurized canister) before pumping it back into your aquarium through a spray bar or spillway.
One thing that makes canister filter stand from the other types of filters is the greater quantity of filter materials it provides for use and a higher degree of flexibility in relation to the filter material of your choice.
In other words, it offers you mechanical, biological, and chemical filtration—depending on the type of filter media you choose to use in the filter.
The TOP benefits of using canister filter media to clean water in your aquarium include:
Let’s discover the 10 best canister filters you can get on the market today…
Our Best Canister Filter Picks:
1. Penn Plax Cascade Canister Aquarium Filter
- CASCADE CANISTER FILTER FOR FRESHWATER OR MARINE ENVIRONMENTS: the Cascade 1000 (CCF3UL) has 3 media baskets, works at 265 GPH, and is recommended for Aquariums up to 100 gallons. It measures 11.5 x 17 x 10 inches.
- STATE OF THE ART FEATURES OF THE CASCADE 1000: ♦ flow valves that rotate 360 degrees for easy maneuvering in even the tightest aquarium cabinets ♦ large capacity media baskets allow aquarists to customize to their media needs ♦ push button primer allows for a quick and easy prime of the filter ♦ includes a spray bar, tubing, directional spout for customization, and filter medium.
- USE ANY COMBINATION OF MEDIA: floss pad for removing particulate matter and a course sponge that provides abundant surface for promoting bacterial growth (to remove ammonia and nitrites) included free with purchase
- SEE BELOW FOR DIAGRAM, THE CASCADE 1000 INCLUDES: ♦ Flow rate control cut-off valves ♦ two independent directional 360 degree rotating valve taps ♦ swimming pool – style hose clamps ♦ quick, easy, push button self-primer ♦ extra-large capacity stackable filter medium containers with lift-up handles ♦ floss pad and coarse sponge included, free with each canister filter ♦ easy lift alignment clamps that release vacuum suction ♦ sturdy tip-proof base
- FILTER MEDIA OPTIONS BY CASCADE AVAILABLE ON AMAZON, SOLD SEPARATELY: see below for details, sold separately is media such as: bio-floss, bio-sponge, bio-rings, filt-a-pack pro-z, and filt-a-pack pro-carb-z.
Penn Plax Cascade Canister Aquarium Filter is one of the most popular filters currently available at the market. Ideal for both freshwater and saltwater aquariums, this filter has an intuitive setup and a powerful 3-stage filtration for the maximum filtration of unwanted elements in your aquarium.
The heavy-duty filter system has an exceptional flow rate of up to 265 gallons per hour, making it suitable for aquariums with a capacity of up to 100 gallons.
It focuses on removing not just the physical components but also the chemical and biological elements. The floss pad removes the particulate matter while the activated carbon removes all the impurities and toxins present in water. And the coarse sponge offers an abundant surface area for maximum biological filtration.
The resulting of all this is a cleaner and healthier environment for your pet fish.
With larger capacity media baskets, customizing them to meet your specific needs becomes quite easier. The easy-push primer button lets you hassle-freely prime your filter with a few button presses.
Also included in the filter package is spray bar, directional spout, tubing, and filter media. All these enable you to start using the canister filter as soon as it arrives at your doorstep.
2. Hydor Professional External Canister Filter
- The hydro professional 350 Aquarium External 280GPH Filter is a complete eco-system in a box
- All the biological, mechanical and chemical filtration that any requires for a healthy and long-lived Aquatic experience
- From the easy priming feature to the telescopic intake tubes, everything had been made easy
- Country Of Origin: United States
Hydor Professional External Canister Filter is another top-rated model for cleaning your aquarium water. It’s pretty easy to set up and use. You just push the self-priming button around 3 times, and your filter is ready for action.
What really gives this filter an edge over most of its competition is its rectangular shape. This means increased capacity—enabling the filter to hold more filtration media than the circular models of a similar size. This greater the capacity, the more water will come into contact with the media for maximum filtration.
We also like the ball-valve connections which help significantly minimize back pressure. They also do a great job of adjusting the water flow to ensure you get just the perfect water output for your fish tank. Also worth a mention is the expandable spray bar with up to 4 sections. This enables you to adjust the length as well as placement for the best filtration results.
The complete kit comes with all the necessary filtration media, except carbon. And depending on the size of filter you pick (it comes in a variety of sizes, btw) you’ll get around 2-5 media trays to allow for multi-stage filtration process.
3. MarineLand Magniflow Canister Filter
- 3-STAGE FILTRATION: Water flows through media layers to filter water and ensure a clean aquatic environment.
- FAST SETUP: Water-tight canister lid lifts up for easy removal.
- THREE SIZES AVAILABLE: Comes in 220 GPH, 360 GPH and 360 GPH sizes.
- MARINELAND FILTRATION PRODUCTS: Count on Marineland brand for the most reliable, technically advanced aquariums and accessories on the market.
If you’re looking for the best canister filter for 55 gallon tank, it’s right here! MarineLand Magniflow Canister Filter employs a powerful, 3-stage filtration process to ensure your fish live in a clean and healthy aquatic environment.
Ideal for both freshwater and marine aquariums, the filter takes your fish tank water through a mechanical, biological, and chemical filtration to make it as clean as possible.
It comes with a polishing filter pad which works as a water polisher—removing all the fine debris. The bio-filter balls plus ceramic rings provide a large, multifaceted surface for bio spires growth. Then there’s black diamond carbon which removes all the odors, discolorations, and impurities in your water.
Like the models above, this filter also features an easy, fast prime button to facilitate easy, fast startup. The canister lid translates to a water-tight seal, for spill-free action.
4. SunSun HW-302 3-Stage External Canister Aquarium Filter
- Canister filters for aquariums use high water pressure, from a properly powered pump, to force water through the dense filter media. A pump can draw water from an under-gravel filter, and run it into a canister for double filtration
- 3 media trays capable of handling your choice of filtration media; Comes with an adjustable spray bar. This is a helpful feature if you want to adjust the output flow from the filter
- Convenient self-priming pump that eliminates the need for manual siphoning; Single valve disconnect & priming pump ease routine maintenance
- Provides quiet, efficient filtration for fresh and saltwater aquariums is great for living rooms, offices or bedrooms
Our 4th spot on the best canister filter reviews list goes to the SunSun HW-302 3-Stage filter. This filter has a wallet-friendly price tag but the performance and features it comes with are quite remarkable.
This filter is suitable for use in both freshwater and saltwater fish tanks of capacity of up to 75 gallons. It comes with up to 3 media trays which means it's capable of performing a biological, chemical, and physical filtration in your aquarium.
With an incredible flow rate of 264 gallons per hours, this filter does its job much faster, saving you a great deal of time and energy. And thanks to the adjustable spray bar, you can easily adjust the output flow from this filter.
Similar to most of the other top-rated filters out there, this model comes with a convenient self-priming button to save you the hassle of manually siphoning it to start using it. The filter operates quietly, making it suitable for can use it in living rooms, bedrooms, or even offices.
5. Aquatop CF Series Canister Filter
For fish keepers with fish tanks as big as 125 gallons, consider the Aquatop CF Series Canister Filter as a good choice for you. As with all the other filters that made it to this list, this model is ideal for both freshwater and saltwater aquariums.
One thing makes this canister filter stand from the rest: it comes equipped with a 9 Watt UV Sterilizer. The purpose of this sterilizer is to eliminate the spores and harmful bacteria residing in your aquarium.
Other than the UV sterilization, this unit takes your aquarium water through a 3 stage filtration process for crystal-clear water and a healthy environment for your pets. Included in the box are 3 fine filter pads plus 1 coarse filter sponge which work together to enhance mechanical filtration. Additionally, you’ll get premium activated carbon, bio balls or ceramic rings for enhanced chemical and biological filtration.
Because this filter comes with 3 large filtration media compartments, you’ll be able to add any filtration media you want to. All the necessary installation and plumbing equipment are included in the box for easy, frustration-free setup.
6. SunSun-China HW-304B 5-Stage External Canister Filter
- Good for up to 150 gallon fish tanks
- Dimension: 11" L X 11" W X 17" H
- Flow rate: 525 GPH (2000L/hr.)
- Built in 9 Watt UV sterilizer for controlling algae spores/bacteria and promoting clear water
Halfway our canister filter reviews, we have another external canister filter from SunSun. Unlike its sister above, this canister has a greater flow rate—making it suitable for fish tanks with bigger volumes of up to 150 gallons.
The most notable feature in this particular external aquarium filter is the built-in 9 Watt UV Sterilizer. This helps kill all the algae spores as well as bacteria, resulting in crystal-clear water in your aquarium.
In addition to this, it features up to 4 flexible media trays where you can add your filtration media—like activated carbon bio-balls, or ceramic rings—to achieve maximum mechanical, biological, and chemical filtration.
Using this canister filter is pretty easy, even for beginners. And that’s because it features the convenient self-priming button for quick, easy startup.
7. EHEIM Classic External Canister Filter
- Permo-elastic silicon sealing ring fixed on the pump head for easy and safe closing after cleaning
- Equipped with filter sponges and/or loose filter media
- Accessories included: spray bar, inlet pipe, hose and installation accessories
- Comes complete with filter media (EHEIM Mech & Substrat Pro) and valves
- Permo-elastic silicon sealing ring fixed on the pump head for easy and safe closing after cleaning
If you’re still on the hunt for a good canister filter for 55 gallon tank, EHEIM Classic is also a perfect choice. This filter comes with a compact size, so it’s also ideal for fish keepers who also want to save as much as possible.
We like the fact that this filter comes with the filter media included (the EHEIM Mech & Substrat Pro), which means you can start using it right away. This filter takes your fish tank water through a mechanical-biological purification. This is a single process which involves water filtration and enrichment with oxygen.
A set of accessories is also included in the filter for easy, quick setup. These accessories include a spray bar, inlet pipe hose, and other essential installation items.
The permo-elastic silicon sealing ring on the pump head facilitates safe and easy closing after cleaning. Above all, this filter runs quietly and has a solid build quality to ensure it lasts a lifetime.
8. Fluval Canister Filter, FX6 Filter
- Multi-Stage Filter that produces healthy aquarium water, freshwater or marine aquariums
- Features Smart Pump Technology for optimal filter performance, efficiency and management
- Self-starting filter-just add water and plug in. Head height (maximum): 3.3 m (10.8 feet)
- For aquariums up to 400 gallons
Do you have a large aquarium system with a capacity of up to 400 U.S gallons? If so, this high-end Fluval Canister Filter, FX6 Filter is exactly what you need to provide a healthy and comfortable living environment for your marine or freshwater pet fish.
The compact, yet powerful, canister filter has a pump output of up to 925 gallons of water and an exceptional flow rate of 563 GPH. This is what makes it the perfect choice for larger fish tanks.
It presents you with a removable stack of super capacity media baskets (each can hold up to 5.9 liters of media) where you can easily place your preferred filtering material. The baskets are also thoughtfully engineered to help eliminate water by-pass, increasing the filtration efficiency.
The instant-release T-handles allow you to effortlessly lift and separate the media baskets for easy routine maintenance.
Something else that puts this filter on the map is the Smart Pump Technology which makes use of an electronic circuit board to continually monitor the filter for optimal performance. The self-priming feature makes the filter easy to start. With a height of 12 inches, this filter will easily fit under most of the aquariums.
9. Polar Aurora 4-stage External Canister Filter
As we draw closer to the end our top-rated canister filter reviews, we have another filter ideal for fish tanks as large as 200 gallons. The Polar Aurora Filter boats of an exceptional flow rate of up to 525 gallons per hour which qualifies it for use in the high volume aquarium systems.
Just like we’ve seen in most of the other filers on this list, this model purifies your aquarium water by taking it through multiple stages (4, to be precise). It comes equipped with 3 large-capacity media trays which are capable of handling any filter media of your choice. Once stocked with different media, the trays will form a 3-stage filtration process, through which water gets stripped off all the unwanted physical and soluble components.
The 4th stage involves using the integrated UV sterilizer to remove the bacteria and algae spores in the water to make it even cleaner.Since this filter also features a convenient self-priming pump, you won’t have to manually siphon it to start it. Single valve disconnect promotes easy quick maintenance. The adjustable spray bar comes handy when you want to adjust filter’s output flow.
10. Tech'n'Toy SunSun HW-603B 106 GPH 3-Stage Canister Filter
- Good for up to 20 gallon fish tanks
- Dimension: 6.5" L X 6.5" W X 11" H
- Flow rate: 106 GPH (400L/hr.)
- Pump Power: 6W
- Includes filter pads, hoses and all parts to get started
If your fish tank has a volume of 20 gallons or less, this small canister filter is an excellent pick for you. Being one of the smallest canister filters on the market, you expect it to come with an affordable cost.
The filter has a flow rate of up to 106 gallons per hour, which is just the right rate for your 20-gallon fish tank. It purifies your aquarium water in 3 filtration stages—to ensure maximum removal of all physical, chemical, and biological elements that might contaminate the water and affect the health of your fish.
The easy to install canister filter is great for both marine and freshwater fish. It’s also incredibly easy to set up and comes with all the necessary parts, including pads and hoses, to allow you to use right away.
11. Finnex PX-360 Compact Canister Aquarium Filter
- Filtration media includes activated carbon floss pad, sponge and ceramic rings
- Perfect for both Aquatic and Turtle Aquariums up to 25 gallons
- Completed accessories include durable water intake strainer, spray bar and filter hanger
- Video: http: //www.youtube.com/watch?v=dKF-CzLFuKk
- 2' Lift available
If you have a slightly larger fish tank of volume 25 gallons, we recommend you to consider this Finnex PX-360 Compact Canister Aquarium Filter. You can use this filter in both freshwater and saltwater aquariums.
This filter employs a vacuum tight force filtration to make your fish tank healthier and cleaner. It comes with different filtration media—namely activated carbon, ceramic rings, and sponge—which work together to remove all the physical and soluble unwanted components in your fish tank. Since it has easily removable filtration chambers, adding or removing the filtration media is easy.
The filter boasts of a powerful top mounted sealed motor with a flow rate of 95 gallons per hour. This is just the right flow rate for your 25-gallon aquarium.
A myriad of accessories also comes with this filter package to ensure you can start using right away, without having to spend on any additional parts. These accessories include a durable water intake strainer, filter hanger, and a spray bar.
12. API FILSTAR XP Aquarium Canister Filter
- Contains one (1) API XP FILSTAR XP FILTER SIZE XL Aquarium Canister Filter 1-Count Box
- Provides very powerful filtration for crystal clear water and healthy environment.
- Designed with self-priming & quick disconnect features to allow safe and easy stop & start of the filtration when maintenance is needed, anti-airlock system to prevent unexpected filtration stops, and anti-noise feature to prevent vibration against cabinet/floor.
- Combines strong flow rates with large capacity for filtration media that removes compounds, colors and odors 3x more effectively than carbon alone.
- Allows the use of various filtration media available in the API range, and meets your specific freshwater and saltwater requirements.
Last in our list of top-rated aquarium canister filter reviews, we have the API FILSTAR XP Aquarium Canister Filter. This is a high-end filter that delivers an extremely powerful filtration process to ensure crystal clear water and healthier environment for your fish (whether marine or freshwater).
The filter’s exceptional performance results from combining strong flow rates (up to 450 U.S. GAL/h) with superior filtration media which eliminates compounds, colors, and odors that activated carbon cannot remove. It takes your aquarium water through a 3-stage filtration process for mechanical, biological, and chemical filtration. What’s more, it offers you an extra-large filter media capacity to let you add various filtration media that meet your specific filtration needs.
With the self-priming feature, starting this filter becomes easier and safer than ever before. The maintenance part is also easy, thanks to the quick disconnect feature which prevents accidental water flow during maintenance.
Despite the powerful filtration process, this filter operates quietly, meaning it won’t turn out to be a source of distraction in your office, living room or bedroom.
How To Buy The Perfect One For You?
If you want to easily and quickly find the best aquarium canister filter for your fish tank, here are the SIX crucial factors that you should look for:
1. Tank Capacity
First and foremost, you need to determine how much a tank volume the filter you’re going to buy can handle.
Luckily, different filter manufacturers offer you the recommended tank size to go with their filter models. Make sure you check this crucial info to get to know if a filter is suitable for your aquarium.
If you don’t get this info on the product description part, you can go ahead to contact the customer support to eliminate guesswork.
2. Filtration Process (Media Trays)
A good canister filter should also come with media trays for all the 3 stages of filtration—mechanical, chemical, and biological filtration.
In other words, never go for a filter that offers less than three purification stages.
While still on it, it’s important to ensure the media trays that come with your canister filter are spacious. This will enable you to put your preferred amounts and type of filter media for maximum filtration of your specific fish tank.
3. Flow Rate (Pump Output)
While this factor is directly related to the previous factor, we saw it better to explain it separately.
The flow rate refers to how fast your aquarium water cycles through the filter pump, and is expressed in gallons per hour (GPH).
Ideally, the flow rate should be 4x the size of your tank (meaning water will cycle 4 through it 4 times per hour).
4. What’s Your Budget?
It’s also important that you have a set budget that you’re willing to spend on the canister filter.
And when setting your budget, make sure you stay within the range of $50 to $300. This is price range within which you’ll find a good performance canister filter based on your tank size.
If you’re on a tight budget, don’t sacrifice affordability for quality. Too cheap filters might not clean your aquarium water well.
Make sure the filter you buy isn’t just affordable but also has what it takes to provide a clean and healthy environment for your fish.
5. Noiseless Operation
Nobody would like a loud aquarium filter, especially if your fish tank is placed in the bedroom, living room, or even office.
Such a filter will be a source of distraction and will see you through sleepless nights.
Make sure you buy a filter whose motor operates quietly.
And don’t just believe what the manufacturer says about the filer noiseless operation; go through the previous user feedbacks to get firsthand info on the quietness of the filter.
One thing you might not know about canister filters is that they can be quite bulky.
For this reason, we recommend you to first analyze how much space is available in your home (where you’ll be placing the filer) before buying a filter.
With the size details at hand, you can then check the dimensions of various filters at your exposal to ensure you find a model that will comfortably fit in the available space.
If you’ve limited space, then you’ll need to look for a small canister filter. With ample space, you can go for any size of the filter, provided it meets your selection criteria.
Additional features to look for in a canister aquarium filter:
Canister Filter vs Power Filter
A canister filter is just one type of aquarium filter. There are several other types of filters you can use for your aquarium, like the power filter.
There has been an ongoing canister filter vs power filter debate seeking to establish which of the two is a better choice for cleaning the water in a fish tank.
Below, we’ll compare the two filters to help you decide which one best fits your needs.
To make this part easier for you to comprehend, we’ll prepare the two filters along these lines:
Installation and performance
A typical power filter is designed to hang on the back of your fish tank. To set it up for use, all you need to do is plug it in and turn it on.
Its integral pump jumps into action, drawing water from your aquarium via a lift tube and passing it through the filter cartridge for purification.
After the water is passed through the media and filtered, it’s then released back into the tank through an overflow or spillway.
As you can easily tell, the water hitting the air on its way back out will lead to some evaporation (or water loss), so you’ll need to refill your tank more frequently to replace the lost water.
Canisters filters come with tubes that you submerge in your fish tank. Using an integral pump, the water is then drawn through a lift tube and into an external filter chamber/canister where it is taken through different filtration media for thorough purification.
Depending on the type of media you’re using, the water will undergo mechanical, biological, and chemical filtration.
After the water is purified, it’s taken back into the tank via the pump. The water transport system in canisters is sealed, so there’s no possible water loss through evaporation or any other means.
The overall maintenance process for power filters is quite easier than in canister filters. You simply need to remove the carbon filters or any other types of media you’re using to ensure continued filtering effectiveness.
You don’t have to take the filter off your tank back unless you’re suspicious that something is wrong with the device’s water suck up mechanism.
As for the canister filters, you’ll need more time and effort to maintain them. You’ll need to take them apart, drain them, and put them back together. You’ll also need to regularly rinse or replace some of the filter media, which means spending money.
Power filters are quite affordable and cost around 10-50 dollars only. If you’re lucky enough, you can even get a power filter alongside your aquarium setup. The models costing you around $10 are great for small fish tanks with a volume of 5-10 gallons. At the price of $50, you’ll get a good filter for larger tanks, say 50-100 gallons.
Canister filters, on the other hand, aren’t cheap. A good quality model on the lower end of the cost spectrum will cost you around $50 while a high-end model will cost you as much as $300.
Power Filters: They’re easy to install and require very little maintenance. They’re also quite affordable compared canister filters. Unfortunately, they’re not as powerful as canister filters and tend to take up considerable space inside your fish tank.
Canister Filters: They’re also easy to set up and are more efficient at filtering your aquarium water and stay out of the way (so they don’t take up any space inside your tank). However, these filters usually require effort to maintain. They’re also bulky and costly.
DIY Canister Filter: How To Build At Home?
It’s possible to come up with your own aquarium canister from scratch instead of ordering a readymade model.
The benefits of making your own canister are pretty obvious—you’ll get to learn something new in the process and save a significant amount of cash.
In the following video, you’ll be taken through step by step guide on how to come up with your own filter.
(The entire project will cost you approx. $50)
How It Works?
A canister filter works by drawing water up a lift tube and out of your aquarium into an external (filter) chamber/canister.
Inside the canister, the aquarium water is then taken through various filtration media to purify it and make it healthier for your fish.
Keep in mind that the direction of water flow tends to vary from model to model (or from different brands). The flow can be top to bottom, bottom to top, center out, back to front, or even outside in.
Inside the filter chamber, your water undergoes mechanical, chemical and biological filtration…though this will depend on the type of media you choose to put in the media trays.
After the water has gone through the filter chamber, it then gets pumped back into your fish tank. Most of the canister filters come with an integral water pump to handle the water pumping job. Only a few of them require you to use an external pump.
As you continue using your canister filter, there are a few things to keep in mind as explained below:
1. You can easily configure your canister filter to offer mechanical, biological, and chemical filtration. As you’ve seen from our canister filters review list above, nearly all of them come with super capacity media trays to enable you to customize what type of media gets into them.
2. You should also make a point of replacing the carbon media frequently. This is because carbon that has become saturated with waste can start releasing toxins into your aquariums. Besides, replacing carbon with a new one will ensure continued efficient filtration.
3. If you’re medicating your fish tank, be sure to remove the carbon media first. Carbon is capable of removing the medicated in under an hour, meaning your fish might not get treated.
4. Canisters filters can be the most efficient filters for your aquarium if you use and maintain them correctly.
Which Canister Filter For Turtles?
If you’re keeping turtles as well, you might be wondering if it’s okay to use the canister filters for fish tanks to clean their water as well.
Though both have many similarities, they require a different type of care (including a different canister filter from that you’d normally use for a fish tank).
Turtles are usually larger than fish and tend to produce more waste and other byproducts compared to the fish.
That being said, you’ll need to use a more powerful canister filter for turtles. The filter should come with an adequate flow rate to help turn the water in your aquarium for at least 5 times every hour.
But getting a powerful canister for turtles is only part of the task…
You’ll also need to ensure that the filter you go with have multiple, larger capacity media trays where you can put the type and amounts of filter media of your choice (or one that meets the turtle aquarium water purification needs).
Another important thing to consider when getting a filter for turtles is multi-stage filtration capabilities. With multiple media trays, a filter will enable you to put the type of filters that will perform mechanical, biological, and chemical filtration on the water.
A filter that comes with an integrated UV sterilizer is also worth consideration as it’ll limit the growth of algae spores and bacteria in your aquarium.
Additional factors to consider when looking for the perfect canister for turtles include your budget, amount of space available for the external filter, and your skill level in using aquarium filters.
Providing a clean and healthy environment for your pet fish should be your top priority when it comes to showing care for your pets and ensuring they live happily.
Luckily, using a canister filter for fish tanks will make your job of cleaning the aquarium easier. It takes the water through a multi-stage filtration process for maximum removal of all the physical and soluble wastes that can risk the health of your pets.
Having discussed all the crucial details you ought to know about the canister aquarium filter in this guide, we’re confident that you’ll have an easy time choosing the most suitable model for your specific aquarium.
Our list of the 10 best canister filter reviews has the 10 most popular filters that will do an excellent job of purifying your aquarium water.