If you inadvertently put a nail into a pipe, don’t be tempted to immediately pull it back out. It’s all too easy for this to make matters worse. A nail in a pipe quite often only leaks slowly, whereas removing it lets the full force of the water pressure take effect.
Turn off the water to the affected section and drain it down.
Then remove the nail but prepare for collecting any residual water there may be in the pipe.
Refer to the section on repairing a leak
Before hammering in nails, use a pipe and cable detector to establish what’s beneath a surface you are intending to nail or screw into.