DIAGNOSIS The most common cause is an air lock in the system or the filter cartridges weren't pre-soaked, causing high initial flow restriction.
FIX First, purge the air. Open the filtered water faucet fully. Then, slowly open the blue bypass valve on the unit for 30 seconds to let air and water mix flush through the faucet. Close the bypass valve. If pressure is still low, shut off water, remove filters, soak them in a bowl of water for 15 minutes to pre-wet the media, reinstall, and flush for 5 minutes.
IF THAT DIDN'T WORK Check for a kink in the 1/4" polyethylene tubing running from the unit to the faucet, especially behind the sink cabinet. A sharp bend will crush the soft tubing.
HEADS UP Normal pressure drop for this system is about 20-30 psi. If your incoming pressure is already low (below 40 psi), the output will feel weak.