It's raining, it's pouring!
Being Northerners, we have absolutely bucket-loads of experience of the vagaries rain, so we consider ourselves to be experts when it comes to creating downpours for stage and TV. We can create anything from tiny little droplets to torrential storm-force rain, or can even rain (fake!) blood. You can have an instant ON/OFF or the rain can ease off gently.
Rain bars need to be hung from theatre barrels or trussing, and catchment tanks can be designed into your set, with the water constantly cleaned and re-circulated. If you require the water to be heated, 3 phase power is required, if not then single phase power is adequate.