Facing a $258 million budget deficit, San Diego City Council members spent an hour Tuesday night delivering an unprecedented public bashing of the region’s main water seller for ever-climbing costs.   Water purchases from the San Diego County Water Authority are the city of San Diego’s second-largest expense and its price increase this year was double what the agency once forecasted. The city’s Public Utilities Department has begun a campaign to alert City Council that growing Water Authority prices threaten to eat up much of the city’s water budget. The result means delays on city water projects and maintenance on 3,000 miles of pipeline, and potential staff cuts which has the labor union representing city public utilities workers shook.