Some of the so-called low water use toilets are advertised to use only 3.5 gallons per flush. Usually the design of the bowl hasn't been changed, however, and often two flushes are needed to remove all solids. Toilets are available which have been redesigned and will do a good job with one gallon or less per flush. This reduction may be more than enough to make the sewage system function again. With a water meter you can determine how much water your automatic washer uses per cycle.
Many washers now have settings to reduce the amount of water used for small loads.
Front loading washers and suds savers use less water than top loading machines. If your sewage treatment system is reaching its maximum capacity, try to spread the washing out during the week to avoid overloading the sewage system on a single day. Baths and showers can use a lot of water. Shower heads that reduce the flow to 1.5 or 2 gallons per minute are available and should be used. Filling the tub not quite so full and limiting the length of showers will result in appreciable water savings.