Increase shower water pressure by removing and cleaning the shower head in vinegar overnight to dissolve mineral deposits. Remove the built-in flow restrictor from inside the shower head. Check the shut-off valve ensuring it is fully open. Install a high-pressure shower head designed for low-flow systems. For whole-house low pressure install a pressure booster pump. Inspect pipes for corrosion or leaks reducing pressure. Clean or replace the shower valve cartridge if pressure drops during temperature adjustment.