Long-Term Debt - Schedule of Long-term Debt Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
Debt Instrument [Line Items]
Total debt	$ 1,901,201	$ 1,719,824
Unamortized debt premium and discount, net	(1,644)	(56)
Unamortized debt issuance costs	(9,234)	(9,216)
Current portion	(23,504)	(3,648)
Total long-term debt, less current portion	1,866,819	1,706,904
H2O America
Debt Instrument [Line Items]
Total long-term debt, less current portion	557,832	557,430
H2O America \| Senior notes
Debt Instrument [Line Items]
Total debt	$ 560,000	560,000
H2O America \| Senior notes \| Minimum
Debt Instrument [Line Items]
Rate	2.47%
H2O America \| Senior notes \| Maximum
Debt Instrument [Line Items]
Rate	3.53%
SJWC \| California Pollution Control Financing Authority Revenue Bond
Debt Instrument [Line Items]
Total debt	$ 630,000	575,000
SJWC \| Senior notes
Debt Instrument [Line Items]
Total debt	$ 560,000	505,000
SJWC \| Senior notes \| Minimum
Debt Instrument [Line Items]
Rate	3.00%
SJWC \| Senior notes \| Maximum
Debt Instrument [Line Items]
Rate	7.20%
SJWC \| Public Utility, Bonds \| California Pollution Control Financing Authority Revenue Bond
Debt Instrument [Line Items]
Rate	4.75%
Total debt	$ 70,000	70,000
CTWS \| Bank term loans
Debt Instrument [Line Items]
Total debt	$ 12,212	14,389
CTWS \| Bank term loans \| Minimum
Debt Instrument [Line Items]
Rate	4.09%
CTWS \| Bank term loans \| Maximum
Debt Instrument [Line Items]
Rate	4.15%
CWC
Debt Instrument [Line Items]
Total debt	$ 448,653	388,672
CWC \| Senior notes
Debt Instrument [Line Items]
Total debt	$ 330,000	270,000
CWC \| Senior notes \| Minimum
Debt Instrument [Line Items]
Rate	3.07%
CWC \| Senior notes \| Maximum
Debt Instrument [Line Items]
Rate	6.46%
CWC \| Public Utility, Bonds \| Connecticut Innovations Revenue Bonds, variable rate
Debt Instrument [Line Items]
Total debt	$ 22,050	22,050
CWC \| Bank term loans
Debt Instrument [Line Items]
Total debt	$ 96,295	96,295
CWC \| Bank term loans \| Minimum
Debt Instrument [Line Items]
Rate	4.04%
CWC \| Bank term loans \| Maximum
Debt Instrument [Line Items]
Rate	4.75%
CWC \| State revolving fund loans \| State revolving fund loans
Debt Instrument [Line Items]
Rate	2.00%
Total debt	$ 308	327
TWC
Debt Instrument [Line Items]
Total debt	$ 149,000	109,000
TWC \| Senior notes
Debt Instrument [Line Items]
Rate	6.27%
Total debt	$ 15,000	15,000
TWC \| Bank term loans
Debt Instrument [Line Items]
Total debt	$ 105,000	65,000
TWC \| Bank term loans \| Minimum
Debt Instrument [Line Items]
Rate	4.01%
TWC \| Bank term loans \| Maximum
Debt Instrument [Line Items]
Rate	6.68%
TWC \| Seller financing debt
Debt Instrument [Line Items]
Total debt	$ 29,000	29,000
Interest rate effective percentage	5.61%
MWC
Debt Instrument [Line Items]
Total debt	$ 101,336	72,763
MWC \| Bank term loans
Debt Instrument [Line Items]
Total debt	$ 85,000	60,000
MWC \| Bank term loans \| Minimum
Debt Instrument [Line Items]
Rate	3.89%
MWC \| Bank term loans \| Maximum
Debt Instrument [Line Items]
Rate	6.47%
MWC \| State revolving fund loans \| State revolving fund loans
Debt Instrument [Line Items]
Total debt	$ 16,336	$ 12,763
MWC \| State revolving fund loans \| State revolving fund loans \| Minimum
Debt Instrument [Line Items]
Rate	0.00%
MWC \| State revolving fund loans \| State revolving fund loans \| Maximum
Debt Instrument [Line Items]
Rate	2.23%

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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