Why Oak Park's Sewer Bill Lives on Your Property Tax Statement, and Why It Keeps Rising

Put an Oak Park tax bill next to one from Agoura Hills and the Oak Park bill carries a charge of about $1,500 a year that the Agoura Hills bill doesn't. That money isn't a tax on the home's value. It is the sewer bill. Triunfo Water & Sanitation District collects its sewer service charge through Ventura County property tax bills, while Las Virgenes Municipal Water District bills its Agoura Hills customers for sanitation as a monthly service charge.

The timing matters this fall. Ventura County mails its annual secured tax bills on or before November 1. The 2026-27 bills are the first to carry Triunfo's fiscal year 2027 rate of $126.23 per month for each residential lot, or $1,514.76 for the year. If you're comparing Oak Park homes with homes across the Los Angeles County line, that one line item changes how both bills read.

A charge on the tax bill that isn't based on value

A California secured tax bill has several parts. The general levy is capped at $1 per $100 of assessed value. Voter-approved special taxes and district direct assessments are added on top. The State Board of Equalization describes the value-based part as 1% plus any voter-approved bond debt service. Direct charges work differently. They are generally flat fees per parcel and aren't calculated as a share of the purchase price.

That difference matters to a buyer. When a home changes hands, the sale generally triggers a reassessment of the value-based tax. The sewer charge doesn't reset with the price. It follows the district's own rate ordinance. So in Oak Park, a $1.2 million home and a $2.2 million home pay the same sewer amount. That also means the effective tax rate on a lower-priced Oak Park home looks higher than the same math would suggest in Agoura Hills.

Sewer isn't the only flat charge on the bill. Ventura County's 2025-26 direct assessment roll lists County Service Area 4 Lights and Landscape for Oak Park at $91,584 spread over 4,835 parcels, about $18.94 per parcel on average. It also lists the Rancho Simi Recreation and Park District Oak Park maintenance assessment at $204,151.46 over 4,860 parcels, about $42.01 on average. Those figures are averages worked out from county totals, so the amount on a given parcel can be different. Sewer is by far the largest of these flat charges.

Priced by the lot, not by the household

The tax bill isn't the only difference between the two systems. Each district prices sewer service on a different basis. Triunfo charges $126.23 a month for each residential lot or separate billing address, whichever is greater, no matter how many people live there. LVMWD's residential sanitation charge, effective January 1, 2026, goes up with household size.

Over a full year, a one-person household served by LVMWD pays $367.08 for sanitation at the 2026 rate. The same household in Oak Park pays $1,514.76 in FY2027. For a household of six or more, Oak Park's flat charge comes out slightly lower. The two rate years don't line up exactly: Triunfo's runs from July 1, and LVMWD's from January 1. Even so, the pattern holds. Oak Park's sewer cost is a fixed cost of owning the parcel, and LVMWD's moves with the number of people in the home. For a downsizer comparing a smaller Oak Park home with one in Agoura Hills, that difference can be larger than many of the factors usually weighed.

Triunfo does have a CARE program. Qualifying sewer customers can receive a $15 monthly credit, $180 a year, applied through the tax rolls.

A rate schedule already set through 2030

Most utility increases come up one board meeting at a time. Triunfo set five years at once. Ordinance TWSD-250, adopted May 19, 2025, lays out the single-residential charge through fiscal year 2030:

1. FY2026: $117.97 a month, $1,415.64 a year
2. FY2027: $126.23 a month, $1,514.76 a year
3. FY2028: $135.07 a month, $1,620.84 a year
4. FY2029: $144.53 a month, $1,734.36 a year
5. FY2030: $154.65 a month, $1,855.80 a year

Each new rate takes effect July 1. A buyer who closes on an Oak Park home this year can already see what the sewer line on the tax bill is scheduled to be starting July 1, 2029, roughly $440 a year more than in FY2026. On its rates page, Triunfo explains the reason for the 7% yearly increases. They are "primarily due to regulatory compliance (principally, the JPA's Pure Water Project), operational costs for the aging system, and the 10-year Capital Improvement Plan (CIP) costs."

Water service from Triunfo is billed separately and also rose on a schedule. For a standard 3/4-inch household meter, the monthly service charge is $41.82 in FY2026 and $42.66 in FY2027. Usage rates were $9.49 per hundred cubic feet for Tier 1 and $10.49 for Tier 2 starting January 1, 2026, then $9.68 and $10.70 starting July 1, 2026.

The project both sides of the county line are paying for

The Pure Water Project explains why Agoura Hills isn't spared from these increases. It is a joint effort of LVMWD and Triunfo. The plant will take surplus recycled water from the Tapia Water Reclamation Facility and purify it with membrane filtration, reverse osmosis and UV advanced oxidation. The purified water then goes to Las Virgenes Reservoir for blending and to the Westlake Filtration Plant for final treatment. Today, Tapia's winter surplus is discharged to Malibu Creek. The agencies say newer nutrient limits there are stricter than conventional treatment can meet, and the project sends that water to purification instead.

Work has started. The Acorn reported in December 2025 that the joint powers authority approved its contract with Walsh on December 8, worth $303.7 million for final design and construction. The Acorn also covered the ceremonial groundbreaking on April 10, 2026. KCLU reported that the plant is designed to take in 7.5 million gallons a day and produce about 6 million gallons of finished water. The project's construction FAQ schedules building from spring 2026 through fall 2028 and the start of operations in spring 2030.

Published cost estimates don't match. In September 2026 the agencies cited a total of about $466 million. A June 2026 S&P Global Ratings report put it at $488.8 million. The September 18 financing announcement reported more than $335 million secured. That includes a $251 million EPA WIFIA loan and $84 million in State Water Board loans and grants, plus a separate $14 million Bureau of Reclamation grant secured in January 2025.

S&P's report assigns 70.6% of the WIFIA loan payments to LVMWD and 29.4% to Triunfo. LVMWD customers carry the larger share, and their bills show it. The one-person sanitation charge rose from $27.35 to $30.59 on January 1, 2026. LVMWD's 2025 rate study proposes $33.04 for January 2027, a step the board must reaffirm before it takes effect. The plant is shared, and so is its cost. Where the two areas differ is in how each district bills it and who ends up paying more.

Where it shows up in escrow

Because sewer rides on the tax bill, it moves through a sale the same way property taxes do. That can surprise buyers who come from places where sewer is just another utility account.

1. Installment timing. Secured taxes are due in two installments, November 1 and February 1, and become delinquent December 10 and April 10. Each installment includes half the year's sewer charge.
2. Proration. Escrow commonly splits the annual property tax between seller and buyer based on the closing date, and that split appears in the closing documents. Since sewer is on that same bill, it goes into the same calculation.
3. Impound accounts. Lenders may require tax reserves in an impound account. Whether a given servicer's reserve covers every direct charge on the bill is something buyers confirm with that servicer.
4. Supplemental bills. A supplemental tax bill issued after a reassessment is separate from the annual bill, and impound accounts generally don't cover it. The flat sewer charge stays the same whatever the reassessment.

FAQ

Does Triunfo's sewer charge apply outside Oak Park? Yes. Triunfo serves more than 30,000 people in east Ventura County, including Oak Park, Lake Sherwood, Bell Canyon, and the Westlake Village and North Ranch parts of Thousand Oaks.

Do Agoura Hills tax bills carry any water district charge? LVMWD lists a $10 annual standby charge on property tax bills for parcels up to one acre, plus $10 for each additional acre or part of an acre. It shows up under direct assessments.

Where can a buyer see the exact charges on a specific home? On that parcel's own tax statement. County roll figures are totals across many parcels, and the 2026-27 bills go out by November 1.

If you're weighing an Oak Park home against one across the county line, The Arledge Group can go through the fixed charges on each property's tax statement with you, so the comparison includes the sewer line. Request your home valuation, and we'll include a look at the direct charges on your own bill.

This article is general information, not legal, tax or financial advice. Consult a qualified professional about your situation.