Reverse Osmosis System Leaking Under the Sink in Mission Viejo: Where to Look and How to Stop It
RO systems under Mission Viejo kitchen sinks have many small tubes and connections. How to find a leak at the feed valve, filter housings, storage tank, faucet or…
Reverse osmosis (RO) drinking water systems are popular in Mission Viejo kitchens, from the original 1960s and 1970s tracts near Lake Mission Viejo to newer homes in the hills. An RO system has many small push-in tubes, housings and a storage tank packed under the sink, and every connection is a possible leak point. Finding the source quickly limits damage to the cabinet and floor.
First, stop the water
Most RO systems are fed by a small valve tapped into the cold water line under the sink. Turn it off. If you cannot find it, close the cold angle stop under the sink. Then dry everything with towels so you can see where fresh water appears.
Common leak points
- Feed valve: the tap or adapter on the cold line. Look for drips at the compression nut.
- Filter housings: worn or pinched O-rings after a filter change are the most common cause.
- Push-in fittings: tubing not pushed in fully, cut at an angle, or scratched.
- Storage tank: the valve on top of the tank or a crack in the tank shell.
- Drain saddle: the clamp on the sink drain pipe where waste water exits. A loose clamp leaks during production.
- RO faucet: the base of the dedicated faucet on the sink or counter.
A dry-paper test
Wrap a strip of paper towel around each connection, turn the feed valve back on, and watch. The paper that gets wet first shows you the leak.
When the leak is not the RO
If everything on the RO stays dry but the cabinet floor keeps getting wet, look at:
- The kitchen faucet supply lines and angle stops.
- The dishwasher supply, which often shares the hot angle stop.
- The garbage disposal and drain connections.
- The wall behind the cabinet, where a supply pipe may be leaking.
A wet cabinet back panel or swollen particleboard with dry fittings above it can point to a pipe in the wall.
Maintenance habits
- Change filters and membranes on the manufacturer's schedule and replace O-rings when recommended.
- Lubricate O-rings with food-grade silicone if the manufacturer allows it.
- Put a leak sensor or drip tray under the sink.
- Check that the cold supply valve feeding the RO actually closes.
Mission Viejo notes
Many Mission Viejo homes have original angle stops under the kitchen sink. If the stop will not close or leaks when turned, it is a common time to look at the condition of the supply lines feeding the kitchen.
Quick takeaways
- Shut the RO feed valve first.
- Filter housing O-rings and push-in fittings cause most leaks.
- Use paper towels to find the exact source.
- Dry RO fittings with a wet cabinet means look at the pipes.
Related reading
On this site, see washing machine supply hoses and angle stop vs shutoff. Neighbors can visit Laguna Hills, Lake Forest and Rancho Santa Margarita, or browse every city at repipeinc.com.
Wet cabinet but the RO is dry?
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Repipe OC, 23821 Hillhurst Drive, Laguna Niguel, CA 92677, (949) 524-2362, CSLB #1087885 C-36.
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Written by Repipe OC · CSLB #1087885 C-36 · 23821 Hillhurst Drive, Laguna Niguel, CA 92677 · (949) 524-2362