The filters are usually the problem. If replacing filters does not restore near-full production, the membrane cartridge may need replacement. If the water production rate suddenly increases, the water tastes different, increases in hardness, or the TDS meter reading increases, the membrane is leaking or possibly ruptured. Regular monitoring is the only way of knowing that an RO unit is functioning correctly. Often the membrane for larger units can be cleaned several times before being replaced.
Manufacturers normally provide cleaning solutions and instructions.
In some models, the RO unit has additional valves and piping to facilitate cleaning, but sometimes the RO system piping must be partially disassembled. The cleaning solution depends upon the materials responsible for plugging the membrane. Acid treatments are common. Use and disposal of the cleaning fluids and flushing of the RO system before returning it to service require extra care. The pumps, gauges and other controls on larger units facilitate monitoring but also require maintenance.