That's almost always a loose housing or a missing or damaged O-ring. Don't worry, it's a straightforward fix.
First, turn off the feed water supply using the shut-off valve on the brass adapter. Then, follow these steps:
- Place the system face-up if possible—it gives you better leverage.
- Use the blue wrench that came with the system. Fit it onto the leaking filter housing.
- Turn the housing counter-clockwise to tighten it. Apply firm pressure. You want it snug, but don't over-torque it.
- Turn the water supply back on and check for leaks.
If that didn't work, the O-ring is likely the issue.
- Turn the water supply off again.
- Use the wrench to remove the housing completely (turn clockwise).
- Inspect the black rubber O-ring seated in the groove at the top of the housing. Make sure it's not pinched, cracked, or missing.
- Reseat the O-ring or replace it if damaged. Lightly lubricating it with a dab of silicone grease (food-grade) can help it seal.
- Reinstall the housing and tighten counter-clockwise with the wrench.
Always check for leaks after any maintenance. If the housing itself is cracked, contact APEC for a replacement.