Tips for troubleshooting an RO filter system

4 min readMay 26, 2023


I have RO filters installed under kitchen sink over the past 7 years. I have replaced many filters (stage 1–3 filters every few months, membrane every year or two). Sharing some tips after years of hands-on experience.

The model I have is this one:

APEC Water Systems ROES-50 Essence Series Top Tier 5-Stage Certified Ultra Safe Reverse Osmosis Drinking Water Filter System, 50 GPD

New Unit Installation

I find the manual that comes with the unit very helpful. For those who are visual learners, there are videos on YouTube with step-to-step instructions. So I won’t repeat here.

The only tip I want to share is to turn OFF the water tank when flushing out a new unit (or new filters). i.e. water should not flow through the yellow tube when you are flushing new filters. Reasons below.

It takes about 5–10 minutes to flush a new unit (you can measure the quality of the filtered water with a $10 TDS water meter). If water flows into the tank while the new filters are flushed, it’ll collect water of lower quality in the tank. Those will be diluted with cleaner water over time. But still, why collect them.

Most Common Issue: Constant draining

When tap water runs across the unit, some waste water would be produced and runs into the drainage tube (black in this model).

If you hear constant draining (more than 5 minutes or so), something’s not right. To confirm the noise comes from the draining tube (not the other tubes), you can wrap your hand around the drainage area. If you hear less noise, it means water is constantly running down to the drain.

I searched online (YouTube) for “reverse osmosis always draining” and found some good instructions. Unfortunately they didn’t solve the three unique problems I had below.

  1. black (drain) tube was connected in the wrong direction

The black tube is the only tube with flow control. There’s a sticker wrapped on it that says “do not remove”. The sticker should be closer to the filters, not the sewage (where you drilled the hole on). If you installed it in the opposite direction, flow control would not work and the pressure in the unit would cause water to flow freely out of black tube.

When a new unit arrives, the black tube is pre-connected on the filter side. If you leave it alone, it’s hard to get this wrong. Our general contractor somehow got it wrong and he ‘fixed’ it by connecting the other tubes to the wrong endpoints until water stops flooding out. He also changed the orders of stage 1 to 3 filters, the sediment (cotton) filter was black when I took it out (which came from the carbon filters). It should look rusty if installed as the first stage.

When I first tested the unit with a TDS meter, the ‘filtered water’ had higher readings than the tap water. I was swearing hard while I fixed all the connections and filters. And for a moment I wondered if my contractor was trying to poison me.

2. unit is not operating at the right pressure

You need at least 40 psi from the inlet. Operating at low pressure will cause the unit to drain constantly. If your tap does not supply sufficient pressure, you can get a ‘RO booster pump’.

Don’t skip the small tap that connects to the inlet of the unit. I’m not sure if that tap caps the max pressure. You need the tap during maintenance (filter replacement). And especially during water outages, which brings up the next tip:

3. red (inlet) tube has rusty water stuck inside

The red tube connects the small tap to the RO unit (the inlet tube).

There was one time we had a water outage for several days. When water is restored, rust has built up in the pipe and it took a while to flush those out from all the taps.

It’ll be good to turn off the RO filter tap during water outages. And turn it back on AFTER you flush the rust out of the main tap. Unfortunately we didn’t. It was very hard for the filter unit to flush those rust out. So it was constantly draining to get rid of the rusty water.

One way to flush the rust out of the RO filter is to:

  • prepare a tub below the unit to collect splashing water
  • pull the red tube out (expect to see rusty water running down)
  • let it run until it’s running clear water, then push it back

Words of Advice

It’s tedious but not difficult to install the unit. It just takes patience. I would advise against letting a general contractor install it who may be rushing it and skipping many essential steps in the instructions (mine has brought me more work in the end).

Hope these tips help you to save some bucks on water bills, while enjoying healthy and clean water.