Step 8 · Turn On Water and Test for Leaks
This is the most critical step. With the access panel still open, go to the shut-off valves and turn them on SLOWLY. Listen for any sounds of rushing water. Return to the access panel and use your headlamp to meticulously inspect every single connection point you touched: where the supply lines meet the shut-offs, where the supply lines meet the faucet handles, and where the mixer hoses connect the handles and spout. Place a dry paper towel under each connection to make spotting tiny drips easier. Turn the faucet on and off from the top, running both hot and cold water, and inspect all connections again while the water is running and after it's shut off.