Oahu's drinking water depends on electric pumps that mostly lack backup generators, leaving residents at risk of losing water in a big storm or hurricane.

• Oahu needs 180 pumping and booster stations running on Hawaiian Electric power to move water to a million people, but only about 16 emergency generators are on hand.
• When power goes out, tanks stop refilling, and neighborhoods like Mililani Mauka can lose water for hours or days.
• Generators go first to systems that supply hospitals and the most people, so smaller areas wait.
• Buying and staffing generators for every station is not realistic, so residents are told to store water at home ahead of storms.
• Rural areas along the coastal highway are most exposed, with one or two roads in and power lines above ground.
• Heavy rain has come in short bursts that run off to the ocean instead of soaking into the aquifers.

Outlook: With storms rolling in every week or two this season, more outages are likely, and the focus turns to hardening pump stations and adding portable generators.