The pre-fabricated concrete block that anchors the light to the bottom of the pond, pool, or fountain is made specially for the job and is sold separately. The cable is attached to a transformer that reduces regular 120 voltage to 12 or 24 volts. Plug the transformer into an outdoor GFCI receptacle. You can purchase this receptacle at any home improvement center also. Because you probably won't want to keep plugging in the unit, especiall when it gets cold outside, place a plastic waterproof cover over the receptacle to keep it plugged in and protected all season.
Most transformers have a switch that turns the light on at a preset time.
Using color lights will make the fountain, pool or pond more attractive. You can buy the special bulbs and filters for your project at your local home improvement center. Make a connection between the underwater light wires and the transformer. With the type of transformer shown above, attach crimp-on connectors by squeezing them onto the wires with a combination tool. Then screw each lead to the appropriate terminal on the back of the transformer.