I wash when the basket gets full. My nappies load is generally a half load, but I can't help that. If I wait until there is a full load, both buckets are full to burst and I'd pass out from the smell. Some days I wash several loads, but that's when sheets and towels get done too. Which reminds me, I'm going to put our sheets on and I forgot to get my daughter's sheets. Will do that in a sec. But I do try to wash only when necessary. We haven't got our water bill yet, so have no idea what our usage is.