Mayor Bruce Smith said the council had taken legal advice and was following a process.
He expected a final decision would be made early next month.
Mr Smith said the delay would not affect the $285,000 Ministry of Health drinking-water subsidy that the council was in line to receive for the Kumara upgrade.
Neither plant currently meets national drinking-water standards. Kumara was recently on a ''boil water'' notice for almost a month.
Mr Smith said he understood the council had until June 30 to let the contracts and get under way with the work in order to keep the subsidy.
The two options the council now faced were either sticking with the successful tenderer, (TES), or alternatively going back to tender.
Five contractors - Filtec Ltd, Process Flow Ltd, Service Engineers Ltd, Southwater, and Techno Economic Services - were shortlisted from an initial list of 49 for the water contracts.
TES tendered the lowest price at $459,000, which it then dropped by $57,000. It scored the lowest in experience and track record (15 per cent) but the highest overall at 85 per cent based on a mixture of design, management and price.
- Greymouth Star