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Reverse Osmosis Technlogy Water Education
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Pure water still tastes like Tap water:

The first thing to check would be if the reverse osmosis membrane was installed. The membrane is the heart of the RO unit and it is the component that removes most of the contaminants and impurities in the water. If the membrane is installed, please make sure the first 1-2 tanks of water have been completely flushed out. The new filters on your system needs to be flushed out before use.


If the tank has been flushed out, use the TDS meter to check the tap water vs. pure water TDS. RO units will remove 90-95% of contaminants and impurities in the water. If the pure water is not at 90% or higher, please contact an APEC technician for assistance.

There is a leak at the Tank ball valve connection

If you are experiencing a leak from where the tank ball valve attaches to the tank stem, you may not have applied enough Teflon tape to the stem when you first installed the valve. To correct this issue, flush out any water that may of filled the tank, then remove the tank ball valve. Apply 6-8 wraps of Teflon Tape to the tank stem and re-attach the tank ball valve. Please double check the connection for leaks.

Filter Housing Is Leaking

If you are experiencing a leak from any of the pre-filter housings on the reverse osmosis system, the rubber O-ring may be defective. The filter housing must have an O-ring in order to seal properly. Please review the steps below to address a leaking filter housing.

Please follow the steps below:

Step 1.  Shut off the feed water line to the RO unit. Turn off the tank ball valve by turning the
Blue Cap on the tank ball valve 90 degrees.

Step 2.     Use the filter housing wrench to unscrew the filter housing that is leaking. Make sure the O-ring is seated correctly inside the filter housing groove. You may also want to apply some lubricant around the O-ring. This will help secure the O-ring in the filter housing groove.

Step 3.     Re-attach the filter housing to the RO head. Hand tighten the housing, then  use the filter housing wrench and simply give an additional quarter inch turn. Do Not over tighten the housing.

Step 4.     Open the tank ball valve and feed water line. Check for leaks. If the filter housing continues to leak, please contact APEC technician for replacement assistance.


How to Test RO’s Shut-Off Function:

The RO system should shut off automatically when the tank is filled. When the RO fails to shut off after tank is filled, the waste water will keep running down the drain, depleting the pre-filters and membrane.

See Fig. 16. The Auto-Shut-Off (ASO) valve is located at point C. The Check Valve is located at point E. These two valves control the RO’s shut off function.

If one of these valves fail (valve worn out, clogged, or defective), the system cannot shut off, and the waste water fill keep running non-stop.

Do test #1 and #2 below to determine if the RO can shut off, and if the valves are OK.


Test#1: Can the RO system shut off?

–    Draw 2-3 glasses of water from spigot. RO will start making water to fill tank.

–     Turn OFF the tank’s valve to mimic “tank full”.

–    If your RO feeds multiple output points (icemaker, bathroom, etc), shut OFF those lines.

–    Wait for 3- 5 minutes, then check to see if the waste water stops running.

–    Check waste water by either “listening” or actually taking out the drain line to look at it.

–    If waste water stops running –>  The RO is shutting off properly. Both the ASO valve and the Check Valve are working fine.  Stop testing.

–    If waste water continues to run  –>  Then either the Check Valve and/or the ASO valve is defective.  Proceed to Test #2.


Test#2:  Test Check Valve and ASO valve:

–    Make sure there is some water in the tank (tank not empty).

–     Remove the Black drain line from the drain saddle (so you can check waste flow drainage).

–    Turn OFF the Cold feed water supply.

–     Turn ON the tank valve.

–    Check the Black drain line to see if there is any water draining out from this line.

–    If water does drain out from the black line –> Then this water is coming from the storage tank. This means the Check Valve is broken, it is allowing the water in the tank to back flow out into the drain line.


Solution:  Replace Check Valve  ( see Fig.16 point E )

–    If no water drains out from the black line (no waste water running)  –> That means the Check Valve is OK.  The RO’s non-shut off is caused by a defective ASO valve, not caused
by the Check Valve.


Solution:  Replace ASO valve  ( located at Fig.16 point C )





System Does Not Shut-Off: Waste water runs all day – and Never Stops

–     Input pressure way too low (below 30psi). Not enough pressure to shut off the RO at all —> Check input water pressure. If pressure is below 30psi, need switch to Booster-Pumped RO model. Contact APEC customer service for assistance.

–    One of the shut-off valves are defective, so RO cannot shut off —> Do a shut-off test to determine which valve is defective. Do test as shown in 6)    How to Test RO’s Shut-Off Function.

System Slow Shut-Off: Waste water runs for hours (6-7 hrs) – but Eventually Stops

The most common cause for “slow-shut-off” is insufficient input water pressure. RO needs
sufficient input pressure to shut off promptly.

–    Input water pressure too low (below 40psi). Not enough pressure to shut off RO promptly —>       Check input water pressure. If pressure is low, boost house pressure or add pump to RO.

–    Feed water valve partially blocked, not opened fully, reducing input water pressure to RO —>        Check and fix feed water valve, make sure it is opened fully to allow maximum pressure to RO.

–     Stages 1, 2, 3 pre-filters partially clogged, reducing the input water pressure in RO —> Check stage-1 filter to see if it’s very dirty. If this filter has turned brown or other color in just 1-3 months, that means your input water has very heavy sediments and other clogging agents. Need to replace stage-1 filter frequently.

–     RO busy feeding multiple output points —> If your RO feeds multiple outlets (icemaker,
bathroom, aquarium), the waste water will run as long as the RO is making water to fill the tank and other output points. In this case, it’s normal to hear waste water running.


Tank Takes Long Time To Fill (does not meet claimed GPD)

–    Insufficient water pressure (below 50 psi for non-pump systems) —> Increase house water pressure or add an appropriate pump to system.
–    Low water temperature (below 77 degree F ) —> Increase house water pressure or add pump to compensate for low (cold) water temperature.


Claimed GPD:

The claimed gallon per day (GPD) flow rate for each RO model is rated based on 60 psi input water pressure at 77 degree F water temperature. At this standard water pressure and temperature, the ROES 50 gpd system should make about 1.8 gal of filtered water per hour, the 4-gal tank should fill in 2-3 hours.


Lower water pressure and colder temperature will slow the system’s output to less than the claimed GPD flow rate. Please check your water pressure as the first step in determining the cause of slow flow rate (low GPD).

Sluggish Flow At Dispensing Faucet

–    Insufficient water pressure (see “RO Basics” for explanation) —> Check water pressure. If too low for this chosen RO model, either increase your water pressure or add pump to RO system.

–    Input water to RO is blocked —> Make sure Feed water valve is fully opened and unhindered.

–    Tank not filled yet —> Wait until tank is more filled, takes 2-3 hours average.

–    Low tank pre-charge pressure —> Raise tank pre-charge to 5-7 psi.


No Water at Dispensing Faucet

–    Water supply is off —> Turn on the water supply, or open Needle Valve ( turn needle handle
counter colockwise)

–    Tank’s valve is closed —> Turn tank valve to an “Open” position

–    Output line is crimped —> Remove crimp

–    Incorrect installation —> See Fig.11. Verify all line connections.
–    Tank defective, no pre-charge pressure —> Set tank pre-charge to 5-7 psi.
–    ASO connection Error —> See Fig. 16A and Fig. 16B to reconnect ASO to the correct connection.

The ASO valve has 4 lines connected to it, 2 Reds and 2 Clears. C1 is labeled IN and C2 is labeled OUT on the valve. C3 and C4 are connected to the ends with the 4 screws. Please confirm connections:
•  Stage 3 Carbon:        Red tubing (point B) is connected to C1 (IN) fig.16A
•  Membrane:        Red tubing (point D) is connected to C2 (OUT) fig.16A
•  Check Valve:        Clear tubing (point E) is connected to C3 fig.16B
•  5th stage Tee inlet:    Clear tubing (point F) is connected to C4 fig.16B



Back View

Fig. 16A



Front View

Fig. 16B