Diagnosis
The most common cause is a clogged filter, usually the sediment filter. Low feed water temperature (below 40°F) can also drastically slow production, or the membrane is fouled.
How to Fix It
Check and replace your first-stage sediment filter. If it's brown and packed, that's your problem. Also, check your water temperature. RO systems work half as fast at 50°F compared to 77°F. If filters and temp are okay, your membrane might be scaled or clogged. If it's over 2-3 years old, it's likely time for a replacement.
If That Didn't Work
Check the auto-shutoff valve. A partially failed ASO valve can restrict feed water flow to the membrane, slowing production. You can test by temporarily bypassing it, but that's a more advanced fix.
Heads Up
Production rate is listed as gallons per day (GPD) at standard conditions (77°F, 60 PSI). Your real-world output will be less. The ROES-50 membrane is a 50 GPD membrane, so expecting a gallon per hour is unrealistic unless conditions are perfect.