CHANDLER — Council members were expected on Tuesday to consider raising water and sewer rates for the first time in 20 years as they prepare for what could be a forced bond election.

“I don’t know what the city is going to do with all of this,” city administrator Jim Moffeit said. “They’re going to look at their options. We haven’t adjusted water and sewer rates in a long time.”

It costs residential customers $15 for up to 3,000 gallons of water. For every 1,000 gallons above 3,000, it costs $1.50. After 6,000 gallons, the cost is $3.50. The city could increase those rates by a third at each level.

An ordinance issuing $1.3 million in certificates of obligation to pay for improvements to Chandler’s wastewater treatment plant will be adopted on Aug. 24 if a petition by Howard Taliaferro to force a bond election is found to be invalid.

Certificates of obligation are bonds issued without voter approval. The resolution approved on July 13 calls for payment of the certificates “from the levy and collection of ad valorem taxes ... and from a pledge of surplus revenues of the city’s waterworks and sewer system.” “We have done certificates of obligation before, for about $1.9 million,” Moffeit said. “Part of it was to complete a sewer project, and the other part went into a road-improvement project. Issuing certificates of obligation is not uncommon.

Raising utility rates would generate revenue from every water and sewer customer in the Chandler city limits. Ad valorem taxes would apply only to property owners.

The most critical needs at the treatment plant — installing a second clarifier at the plant and repairing a lift station — are expected to cost about $900,000.

Other work related to those projects, and related expenses such as legal and engineering fees, could raise costs by at least another $100,000.