Contingencies	12 Months Ended
Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Contingencies	Contingencies Condemnation of Properties: The laws of the state of California provide for the acquisition of public utility property by governmental agencies through their power of eminent domain, also known as condemnation, where doing so is necessary and in the public interest. In addition, these laws provide that the owner of utility property (i) may contest whether the condemnation is actually necessary and in the public interest, and (ii) is entitled to receive the fair market value of its property if the property is ultimately taken. Claremont System: On November 4, 2014, voters in the City of Claremont ("Claremont" or "the City") approved a measure authorizing the issuance of $135.0 million in water revenue bonds by the City to finance the acquisition of GSWC's Claremont water system. On December 9, 2014, the City filed an eminent domain lawsuit against GSWC. GSWC does not believe the seizure is necessary and continues to vigorously defend against the potential condemnation. The eminent domain Right to Take trial is scheduled to begin on June 13, 2016. At this time, management cannot predict the outcome of the eminent domain proceeding. The Claremont water system has a net book value of approximately $49.3 million. GSWC serves approximately 11,000 customers in Claremont. Ojai System: In March 2013, the Casitas Municipal Water District ("CMWD") passed resolutions under the Mello-Roos Communities Facilities District Act of 1982 ("Mello-Roos Act") authorizing the establishment of a Community Facilities District, and the issuance of bonds to finance the potential acquisition of GSWC’s Ojai system through eminent domain. At this time, management cannot predict the outcome of the eminent domain proceeding. GSWC serves approximately 3,000 customers in Ojai. Environmental Clean-Up and Remediation: GSWC has been involved in environmental remediation and cleanup at a plant site (“Chadron Plant”) that contained an underground storage tank which was used to store gasoline for its vehicles. This tank was removed from the ground in July 1990 along with the dispenser and ancillary piping. Since then, GSWC has been involved in various remediation activities at this site. Analysis indicates that offsite monitoring wells may also be necessary to document effectiveness of remediation. As of December 31, 2015, the total spent to clean-up and remediate GSWC’s plant facility was approximately $4.9 million, of which $1.5 million has been paid by the State of California Underground Storage Tank Fund. Amounts paid by GSWC have been included in rate base and approved by the CPUC for recovery. As of December 31, 2015, GSWC has a regulatory asset and an accrued liability for the estimated additional cost of $1.4 million to complete the cleanup at the site. The estimate includes costs for two years of continued activities of groundwater cleanup and monitoring, future soil treatment and site-closure-related activities. The ultimate cost may vary as there are many unknowns in remediation of underground gasoline spills and this is an estimate based on currently available information. Management also believes it is probable that the estimated additional costs will be approved in rate base by the CPUC. Other Litigation: Registrant is also subject to other ordinary routine litigation incidental to its business. Management believes that rate recovery, proper insurance coverage and reserves are in place to insure against property, general liability and workers’ compensation claims incurred in the ordinary course of business. Registrant is unable to predict an estimate of the loss, if any, resulting from any pending suits or administrative proceedings.

Contingencies

Condemnation of Properties:

The laws of the state of California provide for the acquisition of public utility property by governmental agencies through their power of eminent domain, also known as condemnation, where doing so is necessary and in the public interest. In addition, these laws provide that the owner of utility property (i) may contest whether the condemnation is actually necessary and in the public interest, and (ii) is entitled to receive the fair market value of its property if the property is ultimately taken.

Claremont System:

On November 4, 2014, voters in the City of Claremont ("Claremont" or "the City") approved a measure authorizing the issuance of $135.0 million in water revenue bonds by the City to finance the acquisition of GSWC's Claremont water system. On December 9, 2014, the City filed an eminent domain lawsuit against GSWC. GSWC does not believe the seizure is necessary and continues to vigorously defend against the potential condemnation. The eminent domain Right to Take trial is scheduled to begin on June 13, 2016. At this time, management cannot predict the outcome of the eminent domain proceeding. The Claremont water system has a net book value of approximately $49.3 million. GSWC serves approximately 11,000 customers in Claremont.

Ojai System:

In March 2013, the Casitas Municipal Water District ("CMWD") passed resolutions under the Mello-Roos Communities Facilities District Act of 1982 ("Mello-Roos Act") authorizing the establishment of a Community Facilities District, and the issuance of bonds to finance the potential acquisition of GSWC’s Ojai system through eminent domain. At this time, management cannot predict the outcome of the eminent domain proceeding. GSWC serves approximately 3,000 customers in Ojai.

Environmental Clean-Up and Remediation:

GSWC has been involved in environmental remediation and cleanup at a plant site (“Chadron Plant”) that contained an underground storage tank which was used to store gasoline for its vehicles. This tank was removed from the ground in July 1990 along with the dispenser and ancillary piping. Since then, GSWC has been involved in various remediation activities at this site. Analysis indicates that offsite monitoring wells may also be necessary to document effectiveness of remediation.

As of December 31, 2015, the total spent to clean-up and remediate GSWC’s plant facility was approximately $4.9 million, of which $1.5 million has been paid by the State of California Underground Storage Tank Fund. Amounts paid by GSWC have been included in rate base and approved by the CPUC for recovery. As of December 31, 2015, GSWC has a regulatory asset and an accrued liability for the estimated additional cost of $1.4 million to complete the cleanup at the site. The estimate includes costs for two years of continued activities of groundwater cleanup and monitoring, future soil treatment and site-closure-related activities. The ultimate cost may vary as there are many unknowns in remediation of underground gasoline spills and this is an estimate based on currently available information. Management also believes it is probable that the estimated additional costs will be approved in rate base by the CPUC.

Other Litigation:

Registrant is also subject to other ordinary routine litigation incidental to its business. Management believes that rate recovery, proper insurance coverage and reserves are in place to insure against property, general liability and workers’ compensation claims incurred in the ordinary course of business. Registrant is unable to predict an estimate of the loss, if any, resulting from any pending suits or administrative proceedings.