A noticeable drop in water flow can be an early sign of a filter, membrane or inlet-related issue. Unusual sounds, visible leakage or frequent stopping are also worth noting. Write down when the problem started and whether it happens every time you use the purifier.
Do not open electrical parts or attempt complex repairs without the right knowledge. Check only simple items such as the power connection, water supply and visible pipe joints. If the issue remains, arrange an inspection with an RO service provider.
Sharing the purifier model and a clear description of the fault can make the service discussion more useful. Mention whether the unit is producing water, rejecting water or making unusual noise.