How To Replace A Reverse Osmosis Water Tank

Easy directions on how to replace a reverse osmosis water tank.

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• Home: DIY • Home: How-To
• Home: Kitchen • Home: Plumbing

Matt Anderson's Take
A Reverse Osmosis system is a great way to get purified water in your home. It's bottled water quality without the cost and waste of plastic bottles.

Reverse Osmosis are easily to install for most DIY-ers out there. There are a variety of brands and systems but they all make water the same way, though my favorite is the Watts Premier brand simply because changing filters is easier and faster than any other system I've ever used and makes almost no mess.

Other than changing filters, an RO system doesn't require much maintenance. But what happens if the pressure of your RO water starts dropping and you've already replace the filters? Chances are good your RO tank has lost pressure.

Look under your sink and you'll find your RO tank which is actually around 4 gallons in volume and intended to hold about 1 gallon of RO water. When you open the RO tap that stored water comes rushing out. If your RO tap rushes out for a few seconds and then slows you may have an issue with the RO tank.

The tank is 4 gallons in volume with gallon used for water and the other 3 gallons for air. Inside, there is a rubber bladder (like a balloon) that is filled with air. As your system makes RO water it enters the take, compressing that bladder. When you open the tap the pressure from the bladder forces water out.

If the bladder lost pressure or has a leak you'll lose pressure at the RO tap. One way to fix that is to use a hand pump (not an air compressor!) and try to put air back in the bladder. The problem with this is that you can easily over inflate the bladder (it only wants a few PSI) and possibly cause damage to other parts of your RO system. You'll also need to disconnect the system to do this. It's a pain and chances are good that the bladder is leaking and pumping it up won't fix it.

Instead, try lifting the RO tank a little bit. Does it feel like a gallon of water in there or is it far heavier and more like 4 gallons of water. If it's heavy, then the bladder probably leaked and there is no fixing it. Replacement if the only option. The good news is that replacing your tank is pretty easy and fairly cheap.

Step 1
Start by buying a new RO tank here. Shut the water off under your sink and then turn on the RO tap and let it empty as much water out as possible.

Step 2
You now need to remove the old tank. To do that, disconnect the plastic hose that goes into the valve on the top of the tank.


These are usually press-fit connections and removing them requires pushing a collar towards the valve while gently pulling the hose out. Don't force. Some valves have a horseshoe looking piece of plastic that prevents you from pushing the collar in, in that case you have to pop the horseshoe out first. Now remove the tank and empty it.

Step 3
If you bought a new valve for the top of your new tank use it. Otherwise, you need to get the old valve from the old tank. It should loosen easily without tools. If it has any white teflon tape inside, gently clear that debris out.


Either way, apply 3-4 layers of teflon tape to the outlet at the top of the new tank. When looking down on the tank you'll wrap the teflon tape clockwise so that it tightens (rather than loosens) when you put the valve back on.


Now put the valve on and gently hand tighten. Don't go crazy here, it's very easy to crack these plastic valve. Just snug it up, you can always tighten more later if it leaks.

Step 4
Put the new tank in place and push the plastic hose back in. Slowly turn the sink water supply back on and check for leaks as you go. If there are no leaks, let it start making new RO water for 20-30 minutes then check again. Try lifting the tank, if it doesn't weigh much the valve on the top of the RO tank might be in the off position so switch it and try again and then let it run for another 20-30 minutes.


Once you're sure it's make water and has filled the RO tank, empty all of that RO water out. I like to do this twice just in case there are any impurities in the tank itself. You're done, hopefully you'll get several more years of out your new tank.
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