I am installing a contemporary waterfall which will be 12' long and 3' high and will flow from under the coping of one of the side walls of a stone planter down the side wall and into a stainless steel or tiled trough. The stone planter box is 3' wide, 12' long, and 3' higher than the surrounding patio. The trough below will be 1' wide, 12' long and 1' deep. We are also going to clad the wall either in stainless steel or granite. How can we keep the water level in the trough constant without resorting to using a ball type auto-fill valve or one of those expensive electronic sensors connected to a solenoid? Or should I simply tell the homeowner to fill the trough with the garden hose whenever it gets low. The trough will be in full sun during the day during the summer months. This installation is in Toronto, Canada. Thanks!