Just months after Gov. Jerry Brown’s plan to shore up California’s water system with two giant tunnels won key approval from regulators, the $17 billion project is running into potential financial problems. The dozens of agencies that have expressed support for the delta tunnels as a way to ensure that they get more reliable water deliveries, from Silicon Valley to the Central Valley to Los Angeles, are supposed to produce financial commitments in coming weeks. Many, however, appear reluctant to sign on.