water pipe detection in bathroom

[magnet 12]

I have to put up a wall mirror on a double brick and tiled bathroom wall.There are water pipes somewhere " chased" into the wall and I don't want to drill into them when hanging the mirror.Does anyone know a way to detect where the copper pipes are?
Mirror is too heavy to hang by hook and glue and would look bad hanging by chain from ceiling.

[DJ’s Timber]

You can get a 3 in 1 detector for for detecting studs, live wires and water pipes from Bunnings, from memory I paid about $20 or $30 about 2 yrs ago