The city of San Diego is creating the county’s first donation program to help low-income people pay their water and sewer bills, which have risen rapidly in recent years. The long-awaited program is expected to shrink the number of water shutoffs in the city and help some low-income seniors avoid having to choose between paying their water bill and buying medicines they need. In a typical month, about 500 of the city’s 275,000 ratepayers are deemed delinquent and in danger of having their service shut off, city officials said.