The specific steps to fix a leaking water line depending on the type of pipe and the location of the leak.  Generally, the first step is to turn off the water supply to the affected area. This can usually be done at a shut-off valve located near the leak or at the main water supply valve. Locate the source of the leak and assess the damage to determine the extent of the repair needed. To avoid any water damage or further leaks, drain the water from the pipes by turning on a faucet at a lower elevation than the leak. Depending on the extent of the damage, you may be able to repair the pipe with a patch or sealant. If the damage is more extensive, you may need to replace the damaged section of the pipe. Once the repair is complete, turn the water supply back on and check for any leaks or water damage.
If you're not comfortable making these repairs yourself, it's always best to contact a licensed plumber to ensure the repair is done safely and effectively.