Commitments	12 Months Ended
Commitments	Dec. 31, 2025
Commitments and Contingencies Disclosure [Abstract]
Commitments	Commitments SJWC purchases water from Valley Water under terms of a master contract expiring in 2051. Delivery schedules for purchased water are based on a contract year beginning July 1, and are negotiated every three years under terms of the master contract with Valley Water. For the years ended December 31, 2025, 2024 and 2023, SJWC purchased from Valley Water 15.9 billion gallons ($120,322), 17.0 billion gallons ($117,698) and 18.3 billion gallons ($111,173), respectively, of contract water. On June 12, 2024, the Valley Water Board of Directors approved treated water deliveries reflecting the contractual delivery schedule reduced by 23% through June 30, 2025. Based on current prices and estimated deliveries, SJWC is committed to purchase from Valley Water a minimum of 90% of the reduced delivery schedule, or 18.9 billion gallons ($148,795) of water at the current contract water rate of $7.872 million per billion gallons for the year ending December 31, 2026. Additionally, SJWC purchases non-contract water from Valley Water on an “as needed” basis if the water supply is available. SJWC operates the Cupertino municipal water system under a service concession arrangement. The system is adjacent to the SJWC service area and has approximately 4,700 service connections. The original agreement commenced in October 1997 and expired on September 30, 2024. Effective October 2024, SJWC entered into a new 12-year agreement with the City of Cupertino subject to an additional term of eight years if agreed to by the parties. SJWC paid an upfront concession fee of $22.1 million in 2024 and agreed to pay, beginning in 2024, an annual investment rent of $1.8 million, subject to annual adjustment based on a specified construction cost index. The concession fees are amortized as reductions to operating revenue over the applicable contract term and the annual investment rent payments are amortized as reductions to operating revenue over the annual period to which they relate. Under the terms of the agreement, SJWC assumes responsibility for all maintenance and operating costs of the system, while receiving all payments for water service. CWC is able, but under no obligation, to purchase up to one million gallons of water per day from RWA, at the then-current wholesale rates per the agreement, $3.3 million per billion gallons as of December 31, 2025. CWC has an agreement with The MDC to purchase water from MDC to serve the Unionville system. The agreement became effective on October 6, 2000 and has a term of fifty years beginning May 19, 2003, the date the water supply facilities related to the agreement were placed in service. CWC agrees to purchase 0.28 billion gallons of water annually from MDC. The rate charged by the MDC at December 31, 2025 was $3.91 per hundred cubic feet. TWC has multiple long-term contracts with the GBRA. The terms of the agreements expire in 2037, 2040, 2044 and 2050, respectively. The agreements, which are take-or-pay contracts, provide TWC with 7,602 acre-feet per year of water supply from Canyon Lake. The water rate may be adjusted by GBRA at any time, provided they give TWC a 60-day written notice on the proposed adjustment. TWC also has treated water supply agreements with the Lower Colorado River Authority and West Travis County Public Utility Agency expiring in 2059 and 2046, respectively, to provide for 350 acre-feet of water per year from Lake Austin and the Colorado River, respectively, at prices that may be adjusted periodically by the agencies. MWC had an agreement with the Kennebec Water District for potable water service. The agreement had previously been in place for 20 years prior to being renewed on November 7, 2020. The renewal contained an initial term of five years and the ability to renew for up to up to 20 years at Kennebec Water District’s option. In November 2025, the agreement was terminated and MWC transitioned from the previously negotiated rate to a standard tariff rate. MWC guarantees a minimum consumption of 0.05 billion gallons of water annually. Through November 2025, water sales to MWC were billed at a wholesale discount of $0.20 per hundred cubic feet of water below Kennebec Water District's tariffed rates. The current tariff rate was $1.51 per hundred cubic feet as of December 31, 2025. As of December 31, 2025, SJWC had 396 employees, of whom 242 were members of unions. In the final quarter of 2025, SJWC executed three-year bargaining agreements with the International Union of Operating Engineers (“OE”), representing certain employees in the engineering department, and the Utility Workers of America (“UWUA”), representing the majority of all nonadministrative employees at SJWC covering the period from January 1, 2026 through December 31, 2028. The agreements include a 3% wage increase provided in 2026, 3% in 2027 and 4.0% in 2028 for the union employees.