If water production has slowed down and most or all of the water is going down the drain: This problem is caused by a few things. It depends on the age of the unit and the type of unit you have. - If you have a new unit, first check the supply connection. Sometimes, it may not be installed properly. This happens especially with the supply valve. Sometimes the needle does not always pierce all of the way through the copper pipe. Also, check and make sure that any flush valves are closed. If these things do not help, check the pre-filters by remove one at a time (making sure you replace the one removed when moving onto the next filter). Normally, it's one of these things that effect new units. - If you have an older unit, it could be time to replace your filters or the ASOV. If the ASOV fails, it can get stuck in a position to allow most of the water to flow to the drain instead of making pure water. Try flushing off the filters first for about 10 minutes. Also, check and make sure there are no clogs in the lines from anything. - If you have a drinking water unit with a pressurized storage tank, then it may be the bladder in the tank. Most people with drinking water systems gauge their flow on how it comes out of the RO faucet. If it slows down, it's probably the bladder tank. If not, please check all of the above. If your water has stopped: Again, this can be caused by a few things and also depends on the age and type of the unit. - For a new unit, check the lines to see where the flow stops. Again, make sure that all flush valves are closed on your unit. If the flow stops after the RO membrane, remove the fitting that the pure water should be coming out at. Check the Teflon tape wrapping and make sure that it isn't covering the check valve (looks like a metal spring). Try blowing in the fitting from both directions. The flow should be letting the air/water out, but not back in. If the flow stopped before the membrane, check which pre-filter it stops at. If it's still flowing through the pre-filters, but not making it to the membrane, check the ASOV/Permeate Pump. - For an older unit, everything you check for on the new unit is the same with one exception: the membrane itself. If flushing and checking all the of the lines does not yield results, then it might be the membrane. Though this can be the case for newer units as well (receiving a defective membrane), the chances of that is much less than if you  have an older unit. - For units with a pressure tank, check everything above. If you cannot find anything wrong with the unit, it may be that the pressurized storage tank bladder has burst. This is a natural occurrence as the tank gets older. Most of the time, this only occurs every 5-10 years of operating. If you have a newer unit (within 1 year), please let us know. Newer tanks should not have that problem. Please note that the Permeate Pump replaces the ASOV. If you have a unit that's flow has slowed or stopped with a permeate pump involved, these test do not change.