At the risk of being punny, some of this is water under the bridge.

For whatever reasons, SAWS has been behind the industry curve in adopting automated meter reading. They still read meters manually. I always have had my suspicions their meter readers are not consistently reading meters every month. When that happens they average the past few months and send that as your bill (CPS Energy used to do the same thing). Where it really gets out of hand is when this happens for multiple consecutive months, and the average data they have on hand is low. When the meter reader finally reads your meter you then have to catch up on your billing, and the next bill you get is outrageous. You will be hard pressed to get SAWS to admit they are not reading your meter every month, but I am convinced it happens a lot. The solution to this is reading your own meter every month and keeping a record to compare against SAWS. It is probably too late for that.

The other thing that may have happened is you may have had a "sick" meter. Over time water meters wear out, and when they do they read low. Most water utilities have something built into their billing software that looks for anomalies in the usage and kicks out some accounts every month for an audit. Sometimes that may mean your old meter that reads low gets replaced with a new meter, and your shocked to find out how much water you actually use. SAWS isn't always transparent about this stuff either.