The Honolulu Board of Water Supply is proposing to raise the price of municipal water over the next four years and have larger users in single-family homes shoulder more of the increase that’s being sought to keep up with expenses.

Board members of the independent city agency voted unanimously Tuesday to solicit public feedback on a draft package of rate increases that it describes as modest overall and a deviation from drastic past increases.

Increases, if approved, would start in mid-2019.

For average residential customers, most of the hike would hit next year and be followed by smaller increases in the three years after that.

Larger residential water users would see higher-than-average rate increases. Residential customers who use the least would see virtually no rate increase or a decrease over the next four years. Small adjustments also are proposed for agricultural water users and commercial property owners.

Overall, higher rates in the proposal would generate an extra $60 million over four years. The current BWS budget for the fiscal year ending in June is $344 million.

The proposed rate changes are the product of a four-year analysis that involved stakeholder meetings and a 10-year projection of spending needed to maintain and improve Oahu’s biggest public water system, which serves about 1 million customers.

“We think we’ve done a very thoughtful and thorough job,” BWS Manager Ernest Lau said in a statement.

BWS is aiming to avoid what it refers to as “rate shocks” that were delivered in the past to catch up on needed system work.

The agency in 2011 hiked rates 70 percent over five years, which followed a roughly 50 percent increase over five years started in 2006. Before that the last rate increase was in 1995.

BWS relies on customer charges to pay all its expenses for managing a system that includes wells, tunnels, pumps, reservoirs and 2,100 miles of pipe. The agency has a goal to replace 21 miles of pipe a year over the next 10 years, or about double the amount it replaces now. Seven years ago 45 percent of pipes, or 840 miles’ worth, were more than 40 years old.

The agency has scheduled four public hearings in April and May to gather feedback from customers about the rate proposal.

“All of our revenue comes from our customers, so we want to hear from them whether we’ve got this right,” Lau said.

One major shift proposed is to raise rates more for single-­family residences than for multifamily residences, because multifamily households pay for a greater share of BWS costs — 108 percent compared with 88 percent for single-­family customers.

The plan also would vary the agency’s monthly charge for a water meter depending on meter size. Currently, that charge is $9.26. That would rise to $12 for meters in most single-family homes after four years. Charges for larger meters would roughly range from $15 to $600 after four years, including $182 for some hotels and $277 for some schools, under the proposal.

Another planned tweak would provide a rate break to residential customers who use less water.

As proposed, residential customers who use less than 2,000 gallons a month would pay $3.70 (multifamily) or $3.79 (single-family) per 1,000 gallons next year compared with $4.42 now.

Currently, there are three rates depending on how much water a household uses: $4.42 per 1,000 gallons for the first 13,000 gallons, $5.33 per 1,000 gallons for use between 13,000 and 30,000 gallons, and then $7.94 for every 1,000 gallons beyond that for single-family homes. The rates for multifamily homes are the same, but the use ranges are lower.

Under the proposal, there would be four tiers with different use levels, including a range from 2,000 to 4,000 gallons for multifamily residences and from 2,000 to 6,000 gallons for single-family residences.

The average single-family household uses 9,000 gallons, and the base cost for that water under the proposal would increase to $40.60 from $39.78 next year and then to $41.82, $44.44 and $47.47 over the subsequent three years. Over four years that increase totals 19.3 percent.

The average multifamily household uses 6,000 gallons, and the proposed base cost for that water would decrease to $26 from $26.52 next year and then eek upward to $26.06, $26.16 and $26.46 over the following three years. Over four years this amounts to a 0.2 percent dip.