The cost is the same whether constant supply from the spigot, or using a bucket. The volume of water consumed is the same; it is the delivery method that is different. Gravity supplies water pressure in your system, the water pressure is from the spigot in my system. And there is basically zero waste with the cups in either system. Just because the spigot is on; does not mean water is constantly flowing. Or...forget the spigot, it is just a valve that is open further back in the system now. Where the water comes out now are the 20 cups...so think of instead of one water hose spigot, there are now 20 spigots that the birds turn on and off when the drink. Follow me?