If you reduce your winter water bill, you will save for the next year on your sewer bill. So, for instance, if you've been meaning to buy a low-flow toilet, put aerators on your faucets, or get a low-flow shower head, now's as good a time as any. If you don't want to replace all the toilets, just replace the one that gets the most use. Designs have improved so much that a water-efficient new toilet works far better than the old water-guzzling varieties. Consumer Reports compares some models. I've heard Eljers are good, and Toto, too. Toto has a 1.28 gallon E-Max model that is excellent. I'm sure there are many others that work well. Gravity flush is more than sufficient. No need for pressurizing chambers, etc.
Another way to save on water bills, and heating as well, is to adjust your water heater so that the water is just the right temperature for a shower. This makes for much less fiddling with hot and cold during showers, and makes it easy to adopt the "navy shower" approach (http://en.wikipedia.org/wiki/Navy_shower). Maybe we should call it an "energy security" shower.
(Initial draft written Feb. 8, 2012)