Cut back on the amount of tanks that you have down in the basement Jeremy and you'll cut back on the amount of water being evaporated.:)
Aren't you up to something like 22 tanks now LOL :D
But seriously lids on everything would help specially the sump but then you run into other issues where the water starts to pool on the underside of the lids, not a big issue on the sump but, you run into issues with light penetration on the display tanks.
Other things that I've done to help would be to lower the ambient temperature of the room and slightly lower the temperature of the tank water.