On paper, there’s enough water for San Diegans for years to come. The exception is in San Marcos. Every five years, urban water agencies across California must prepare reports showing they won’t run out of water. Almost every San Diego water agency projects they will have enough water for the years to come. But the Vallecitos Water District, which provides water to 97,000 people in and around San Marcos, has projected a huge shortage: 3.7 billion gallons a year by 2020. Vallecitos is the only district in the state that projects such a shortfall.