Waterbeds should have their water conditioned every few months. But NOBODY does this. And in the minds of many waterbed owners, there's probably some latent guilt and uncertainty about it. If you offered a door-to-door "water conditioning service" for waterbeds, you'd probably get some takers. The important thing is to make them understand how bad this is for both their bed and for them. Warm water is a breeding ground for all kinds of bacteria and it can be the cause of a lot of otherwise unexplainable sickness. A conditioning kit costs about $20, but the chemicals in it can be bought for pennies in bulk. You should be able to earn $20 per house. One problem with a door-to-door campaign is that only about 1 in 20 houses will have a waterbed. If you could negotiate with waterbed stores and buy a list of customers in exchange for a commission, that would be even better!