Understanding the Science Behind Hydrostatic Water Storage Tanks

Hydrostatic water storage tanks are unique storage tanks used in under-sink RO water purifiers.

But what exactly is a hydrostatic water storage tank, and how does it work?

In this blog post, you’ll dive deep into the basics of hydrostatic or hydropneumatic water storage tanks and how they operate and explore some of the benefits of using this type of water storage solution in water purifiers.

Whether you’re looking to buy a new under-sink water purifier or currently own one, this post will provide valuable insights and information on hydrostatic water storage tanks.

What is a Hydrostatic Water Tank?

As stated above, hydrostatic water tanks are commonly used in under-sink water purification systems. That’s why they are generally referred to as under-sink RO tanks.

These tanks are typically made of stainless steel or any other corrosion-resistant material and are equipped with a bladder that separates the water from the air inside the tank. The pressurized air in the tank helps to push the water out of the tank and to the faucet.

You’ll see how exactly these under-sink RO tanks work in the following section of the post.

One of the main advantages of using a hydrostatic water tank in a water purification system is that it allows for a consistent flow of purified water.

In addition to holding purified water, hydrostatic water tanks also have other features, such as an air valve for repressurizing the tank. These features help to ensure the safety and reliability of your under-sink RO system.

Generally, these storage tanks come in cylindrical shapes. However, they come in varying capacities and sizes. The size of the tank depends on its storage capacity.

How Do Hydrostatic Water Storage Tanks Work?

Hydrostatic water tanks use air pressure to supply purified water stored in the tank to the faucet above your sink.

Hydrostatic tanks have two separate chambers, an air chamber and a water chamber, divided in the center by a bladder or diaphragm.

Working of Hydrostatic Water Storage Tanks

As the storage tank fills with purified water, the weight of the water pushes this bladder down into the air chamber and compresses that air.

As that air compresses, it increases the pressure inside the tank. This pressure pushes the purified water out of the tank and to your faucet.

Without this air chamber, the tank would fill up, but the water would not reach the faucet. Or we’ll have to install a pressure pump, in which case the water would not come out in absence of electricity.

Hydrostatic water storage tanks provide you with purified water without needing any electricity or a pressure pump.

On the smaller tanks, the water is on the top and the air chamber is on the bottom.

Bigger tanks, on the other hand, have water at the bottom and an air chamber at the top. This is so because of the excessive weight of water.

The tank is equipped with a float valve that helps to maintain the proper water level in the tank. The float valve works by opening and closing the water flow into the tank as the water level in the tank rises and falls.

Did You Know?
Hydrostatic water tanks do not store as much water as claimed.

Yes, that’s true.

The mentioned storage capacity is the total volume of the under-sink storage tank.

But as you have seen above, hydrostatic water tanks have an air chamber.

So,
Tank’s actual water storage capacity= Total Tank Volume – Volume of the Air Chamber

Roughly speaking, an 8 litres storage tank, may only hold around 5 litres of water.

Common Issues with Under-Sink RO Water Tanks and Their Solutions

Why there is No or Very Little Water Coming Out of the Faucet?

There can be two reasons behind this problem –
i) The RO system is not working fine because of which it is producing very little or no purified water.
ii) The hydrostatic tank is not working as it should

But, how do you find that?

Finding the problem with your RO system is quite easy. All you have to do is, check the output of water by disconnecting the pipe that goes from the last filter to the storage tank. If there is no flow or water is coming drop by drop then the issue is with your RO system. Call the service engineer.

If the water output is normal then it is the hydrostatic tank that is creating the problem.

Over a period of time, the air will naturally leak out from the air chamber, resulting in lower pressure inside the tank. This will reduce the flow of purified water from the faucet.

This is a natural phenomenon and all tanks will face this issue over time.

How Do You Increase the Air Pressure of the Hydrostatic Tank?

All hydrostatic water tanks feature an air valve, just like the one on your bicycle tyre. And you can fill the air in the tank just like you would inflate your bicycle tyre.

Here is how you do it.

Before you start adding air to the tank, switch off your RO system and open the faucet and run the water until the tank is empty.

Leave the faucet open.

Now remove the cap on the air valve and connect the bicycle pump to the valve. Slowly pump air into the tank. You will notice some water coming out of the faucet.

Close the faucet when the tank is completely empty. Now slowly add air into the tank and check the air pressure with a pressure gauge.

The pressure should be around 7 psi. This is the recommended air pressure for most under-sink purifier tanks.

Please note that the air pressure should not be more than 7 psi.

When Do You Need to Replace Your Hydrostatic Tank?

Hydrostatic tanks used in under-sink RO purifiers are made to last for a very long duration. Most tanks last for as long as 10 years or even more.

But like all equipment, they too can develop problems over time.

If the RO system is working fine but the faucet does not dispense any water even after adding back the air pressure in the tank then it is a clear sign that the tank needs to be replaced.

Also, if you notice water leaking from the air valve when you refill the air or test the pressure, that is also a clear sign that the bladder separating the water and air chamber within the tank has failed. This cannot be repaired, and you will have to replace the tank.

Do You Need to Clean Under-Sink RO Tanks?

Yes, like all wall-mounted RO purifiers, the hydrostatic tank of your under-sink water purifier also needs to be cleaned.

And you must at least clean the RO tank every 6-12 months. This will clean all the slime that builds up over time and ensures the purity and safety of the water you drink.

Relevant Post: How to Clean RO Tank?

Wrapping Up

In conclusion, the ability of hydrostatic tanks to use air pressure to maintain a constant water flow makes them a valuable addition to all under-sink water purifiers. Hydrostatic tanks are as important a part of under-sink water purifiers as an RO membrane.

Hope this post has provided you with all the information about hydrostatic water tanks.

If you have any specific query that is not answered above, please leave a comment below and we’ll be happy to revert back in the next 24 hours.

Thank you for reading.

Pramod

An engineering graduate from a top Indian university, boasts a decade-long expertise in reviewing home appliances, particularly water purifiers. As the Editor-in-Chief of BestROWaterPurifier.in, his insights empower readers with valuable advice for healthier choices in household essentials.

2 Comments
  1. I have AO Smith RO x5. I m receiving TDS from 27 to 30. Is it ok to drink with such a low TDS? Will it affect health?? I have small kids, so I m worried about such low TDS water. Should I go with the same RO or should I replace it? Please suggest me.

    • Ideally, the TDS level should be above 50. But, you need not worry. As water is not the only source of essential minerals like Calcium and Magnesium. We also get the same from the food we eat.

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