I've done this over a dozen times. It's not for the faint of heart. First of all you'll need to use a small spa heater, because the concrete and tile act as a huge heat sink and the water is always cold. Next you have to deal with the building of the jets and system. Using rigid pvc pipe makes a nice skeleton, but flex pvc (below) is easier to get everything lined up. Next you have to worry about leaks. Getting the jets to seal around the brick, block, concrete (whatever) is always a project.

This really is a tough job. Ask anyone who's done one. If you want to do it, don't hire anyone unless they've done one you can see and talk to the owners.

• Flexible PVC pipe