There could be various reasons for a slow water flow in your purifier. Here are a few common ones.
The filter gets clogged due to excess usage or maybe due to improper fittings. Unclog or replace the filter if it is clogged.
The flow can also be affected due to reduced pressure in the Reverse Osmosis (RO) water tank. To solve this problem, increase the RO pressure.
If the incoming water pressure is low. Fix the RO membrane to increase the incoming water pressure.
Bent in tubing can also drop the pressure restricting the flow of water.
It is best to call a technician to fix these problems in your purifier.
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