Quick Answer
Any shower filter adds some resistance, so a small flow reduction is normal. Significant drops usually mean a clogged cartridge, sediment, or an overdue replacement. Flush the filter, check the cartridge age, and replace if past its interval.
Problem
After installing a filter, some users notice weaker flow and worry the filter is faulty — but a modest reduction is expected and a large drop usually points to a loaded cartridge.
Product Recommendation
ZOOSHEN flow rates are published after final validation. Replacement cartridges restore full flow when the old one is loaded.