Grohe faucets have an adjustment setting which increases or decreases water flow rates. When you get the faucet, it is set to the highest setting, but as time goes on, adjusting this setting may be necessary due to sediment build-up or your own personal needs. To adjust the Grohe faucets, the flow rate limiter is the part to focus on. It takes no special skills to access this part, and a plumber or professional is not necessary.
Turn off the water to the faucet by shutting both valves underneath the sink.
Take the handle to your Grohe faucet off. First remove the screw in the base of the handle with an Allen wrench and then pull the handle off the faucet.
Turn the cap, which is the cylindrical cover on the faucet body, a complete half turn or until the slot points upwards, and pull it off the faucet fixture.
Insert the Allen wrench into the top opening in the adjusting lever , the square knob on top of the faucet's cartridge, and turn the wrench towards the left side of the faucet to reduce water flow. Turn to the right side to increase flow.
Repeat the above step as needed until the water flow is set the way you like it.