At first glance Reverse Osmosis drinking water systems can appear somewhat complex. It helps if you know how they work, so I suggest you view my How a Reverse Osmosis drinking water system works video before watching this one on troubleshooting.
One of the most common concerns is very little or no water flow from the drinking water faucet, but when you check, the tank is full, which you can tell by how heavy it is. The usual cause is the tank is low on air pressure or has a torn bladder.

To remedy this situation, follow these suggestions:
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1) Turn off the water flow from the source, shut off the tank and disconnect and remove the tank, I usually take it outside at this point.
2) Find the blue or black plastic cap on the bottom or side of the tank and open it to expose the metal air stem valve. If there is water leaking out of this valve or air is coming out of the shut off, the bladder is torn and the tank needs to be replaced.
3) You need to check the pressure within the tank when it is empty, so open the valve and let the water run until it is empty. If it does not empty fully, connect a tire pump or compressor to push out all of the water before proceeding.
4) Using a low range tire pressure gauge, check the pressure inside the tank, it should be between 6-8 psi, likely it will read 0 at this point.
5) Carefully re pressurize the tank with a bicycle tire pump or compressor to whatever it says on the tank or if nothing is noted on the tank to 6-8 psi. Do not over pressurize as you may burst the bladder!
6) Reconnect the tank and allow the tank to refill and you'll be fine. If you find the tank needs to be constantly re pressurized it is time for a new tank!  Shop here for new tank.