I think you still get charged the same amount of sewage on the water you use no matter how little you chuck away, i know the company i work for in my fulltime job gets charged a lot for serage due to amount of water we use, even though the water which is called sewage/waste water actually go outs cleaner than in came in, thats due to it being a filtration plant, and everything in and out gets filtered over and over, if anything the local water company should charge the company less as the water is better when it leaves