Diamond BarWhat a house pays

Diamond Bar water and sewer rates

Who supplies water to Diamond Bar houses, what it costs, and how the sewer charge works.

Walnut Valley Water District

Walnut Valley Water District, single-family rates effective January 1, 2026: a monthly base rate by meter size plus three tiers per unit (1 unit = 748 gallons); homes in pumping zones 2 and 3 pay $0.30 or $0.55 more per unit.

Use a monthPrice per unit (CCF, 748 gallons)
Fixed charge$41.98 a month
0 to 6 units$4.02
6 to 27 units$5.08
27 to more$6.75
Source
Walnut Valley Water District imports 100% of its drinking water through Three Valleys Municipal Water District and the Metropolitan Water District: about 60% from MWD's Weymouth plant, 39% from TVMWD's Miramar plant and 1% groundwater.
Hardness
Total hardness averaged 234 ppm in the water from MWD's Weymouth plant and 97 ppm in the water from TVMWD's Miramar plant.
Lead
In tap samples from 30 sites in 2024 the 90th-percentile lead result was 0 ppb and no site was above the action level; the District's 2024 service line inventory found no lead or galvanized service lines requiring replacement.

Sewer

County Sanitation District No. 21, which covers all or portions of Diamond Bar, charges $224 per single-family home for 2026-27 and collects it on the property tax roll. The County's Consolidated Sewer Maintenance District, whose service areas include Diamond Bar, charges $78.50 per sewage unit (one single-family dwelling) for July 2026 to June 2027, collected on the tax roll as a sewer service charge.

Ways to pay less

  • Low-income seniors over 62: Safe, Clean Water parcel tax exemption. Owners over 62 who live in the home and head a low-income household can apply for an exemption from the Safe, Clean Water Program special parcel tax; the FY 2027-28 limit is $106,600 for a 2-person household. How: Submit the claim form to the Safe, Clean Water Program by May 1 each year; call 833-275-7297.

Pay or manage it

Sources

  1. Walnut Valley Water District: single-family residential rates 2026
  2. Walnut Valley Water District: rate schedules and classes
  3. Walnut Valley Water District: district overview
  4. Walnut Valley Water District: 2025 Consumer Confidence Report
  5. LA County Public Works: sewer maintenance rates
  6. LA County Public Works: Consolidated Sewer Maintenance District annual report
  7. Metropolitan Water District FY 2026/27 tax rate resolution
  8. Safe, Clean Water Program: tax appeal procedures and guidelines
  9. LA County Public Works Safe Clean Water tax layer description
  10. Safe, Clean Water Program: FY 2027-28 low-income senior exemption form

Checked October 22, 2026. Every number here comes from the public sources listed, matched by our checker.

Rates change every year; this page shows when it was last checked. Nothing here is legal, tax or insurance advice.