For months, a riled contingent of the City’s water customers has been complaining about high water bills.

Complaints duly noted, City officials said recently.

“We’ve been through a very long, hot, dry summer, and there’ve been calls to the utilities center and the mayor’s office, and maybe some of you as well,” Finance Director Shelley Coleman began at a recent study session of the Auburn City Council.

Given Auburn’s summer of discontent, Coleman went on to offer this primer on how one’s water bill gets to be what it is.

First, she said, the City charges its residential and commercial water customers a monthly flat rate. For residential customers, the current base rate is $15.05 per month. Residential water meters are read bi-monthly. While the City bills each water customer the same flat rate per month, it bills water usage, or consumption, every other month. And the latter is subject to tiered-rate billing.

There are 292 large meters within city limits that are read every month, and 13,939 meters that are read bi-monthly.

So, what’s tiered-rate billing?

In 2002, to encourage water conservation, the City paired its flat-rate with a block-rate or tiered system. So, if a customer “breaks through” a certain amount of water usage per month, he or she pays a higher rate, in addition, again, to the base rate.

Over a two-month span, the first seven ccfs used — a “ccf” is 100 cubic feet of water — in terms of consumption is 1,400 cubic feet that counts toward usage. Customers who use what the City here considers an average amount of water benefit from the lower rate, whereas customers who use more water pay in the higher tiers.

Here are the monthly-tiered water billing rates:

• Tier 1: customers who use 0-7 ccf per month over two months pay $2.99 per ccf.

• Tier 2: customers who use 7.01-15 ccf a month over two months pay $3.65 per ccf.

• Tier 3: customers who use more than 15.01 ccd a month over two months pay $4.15 per ccf.

In comparison, the City of Renton’s monthly base rate is $17.60. A customer rises from tier 1, 0-5 ccf, where he or she pays $2.54 per ccf, to tier 2 after exceeding 500 cubic feet of water consumed in a month, or 1,000 cubic feet over a two-month period, which is $3.41 per ccf. Customers who exceed 10.01 ccf per month land in tier 3 and pay $4.30 per ccf.

The City of Kent’s base rate is $13.10. It has a winter rate, 0-7 ccfs for $3.12 per ccf, and a summer rate, 0-7 ccfs for $4.11 per ccf. Usage in excess of 7.01 ccf raises the customer to $4.22 per ccf at the winter rate and to $5.24 per ccf at the summer rate.

Coleman’s primer on water bills comes as the City begins the 2½-year process of replacing the 14,231 water meters within its 23-square mile water service area with an automated meter reading system. The $5.4 million project, excluding tax, will not require a rate increase. Financing for work in 2015 will be from 2013 Revenue Bonds, whereas financing for work in 2016 and 2017 will be from future financing, as determined appropriate by the City’s finance department and approved by the City Council. The City expects a return on its investment in 20 years. The system vendor is Ferguson Water Works.

Here is the anticipated installation schedule:

• 14,103 existing meters

• 213 AMI meters to be installed in 2015

• 5,415 AMI meters to be installed in 2016

• 8,475 AMI meters to be installed in 2017