The plant is now in the process of being commissioned, which is expected to be completed by the second week in November, after which the supply will feed through the network.
It was blessed on Saturday morning, attended by Matahiwi Marae, near neighbours, councillors and the construction teams.
Kaumatua Tom Mulligan and Ratana Church minister Brown Wiki led the blessing, after which Hastings mayor Sandra Hazlehurst thanked mana whenua and neighbours of the site for their support.
"Safe drinking water is our number one priority and the projects being undertaken to upgrade Hastings' drinking water supplies includes our eight small community supplies," she said.
"It is great today to celebrate the completion of the first new water treatment facility."
Hazlehurst thanked community members who contributed to the project including Ray Wiggins who sold council the site and Russell Collins who let them use his paddocks to weld and store 1855m of pipe and the residents on the road who coped with the disruption.
The other small community water supplies being upgraded are Whirinaki/Esk, Te Pōhue, Waimārama, Clive, Waipātiki, Whakatū and Waipatu.