People flock to a Chula Vista parking lot to fill up jugs with water from a colorful kiosk owned by Colorado-based Watermill Express.

The company is one of several competing for customers suspicious of city tap water and fed up with buying bottled water.

Watermill, which runs a few dozen water vending machines across San Diego County, typically pays about $4,000 for the water that comes into its machines – city tap water that must meet state and federal water quality standards to begin with.