Wow, my sewer bill went way up in April (or way down). How are sewer bills calculated?

Sewer rates are recalculated every April, based on the average quarterly water usage during the last three months of the previous year and the first three months of the current year (i.e. during the fall and winter when virtually all water use flows into sewer systems). As a result, some residents observe large fluctuations in their sewer bill from year to year due to their water usage during the preceding winter.