Water was restored on Friday to Hamilton residents who lost their supply when a lightning strike crippled the city's water treatment plant.
A bolt of lightning on Thursday damaged the site's computer, alarm and communication systems.
Residents in the suburbs of Hillcrest and Flagstaff were experiencing low water pressure, and in some cases had no water at all.
City Waters manager, Tim Harty, says the plant was gradually restored to full operation and all systems were up and running by early afternoon.
He says the plant is a complicated site and it would have come to an emergency stop. The company will investigate what went wrong.