Understanding Martinborough Water Supply

–Mark Allingham, Infrastructure and Services Manager, SWDC

During the Martinborough Boil water notice it came to our attention that many in the township were unaware of how the Martinborough water supply operated and why the system is not currently chlorinated.

Martinborough’s system is different to most water systems in that groundwater is extracted from the bores next to the Rumahunga river to the west of town. It is then treated with Ultra Violet Radiation (sun lamps), PH corrected and pumped through the township to the reservoir tanks on the hill above the golf course. The gravity pressure from the tanks and the bore pumps keeps the pressure in the pipes that supply your homes.

Quarterly testing of the untreated groundwater, since 1990, has not shown any indication of bacterial contamination. The last of these routine tests was carried out in December 2018.

The UV disinfection system provides treats the water after it is extracted from the bores and at the point enters the system. The system relies on the premise that nothing else enters the system from anywhere. Backflow prevention mechanisms are fitted on connections throughout the system with the aim of preventing potential sources of contamination

Martinborough’s water:

1. Inside the pipes is a biofilm that naturally accumulates on the pipe walls (like cholesterol in arteries).  
2. The groundwater from the bores contains manganese, this when mixed with chlorine will discolour the water and while completely safe to drink, being blackish in colour is not palatable.
3. As the water is pumped through town to the tanks, the manganese settles on the bottom of the pipes, in the biofilm, and is suspended in the water. 
4. So, if there is a broken pipe or major disturbance to the pipes this can cause either the dark manganese granules or biofilm containing the manganese to be released, this can enter people’s water supply. Manganese is more of an issue in areas of the system where it settles in the biofilm, for example the bottom end of the system (New York St) and where the water travels frequently backwards and forwards between the tanks and the bores; it’s not so much of an issue at the top end of town.