Woodbourne Water Notices

Dropping turbidity levels mean that the UV disinfection unit is fully operational again, and the water is deemed safe to drink. Chlorine is protecting water quality between the water tower and the tap.

Water treatment involves a multi-barrier approach to contamination. The first barrier is the groundwater aquifer and secure borehead which provide an element of filtration and protection from activities on the surface. Water entering the plant is pre-treated through a 10 micron (10 thousandths of a millimetre) sand filter, then a 1 micron cartridge filter. The water is chlorinated to kill bacteria and to protect from recontamination in the network, and also disinfected with ultraviolet (UV) light, which is effective against both bacteria and protozoa. 

The Drinking Water Quality Assurance Rules apply limits on turbidity ensure the proper performance of each of these barriers. For a period in the wake of the recent storm, the turbidity limits associated with the cartridge filter, the chlorination and the UV disinfection were exceeded, meaning that we couldn’t guarantee that they were doing their job.

Requirements for protection against protozoa (such as giardia and cryptosporidium) are measured in log credits. For our 20 metre deep bore we require 3 log credits. The cartridge filter can provide 2 log credits, and the UV system can provide 3 log credits.

Turbidity levels continue to decrease, but right now they still exceed the capability of the cartridge filter meaning that, while it is filtering the water, we can’t guarantee its effectiveness, and therefore it achieves no log credits. However, turbidity has dropped within the UV disinfection unit’s effective range. The UV disinfection unit is now fully operational again, and achieving all 3 log credits that we need. The chlorine we put in the water protects it from any further contamination as it flows from the treatment plant to your taps. We have allowed sufficient time for around two tower volumes worth of safe water to flush through the system, and we are now satisfied that the water supply is safe to drink and use as normal.

You may be aware that we are finishing construction of a new water treatment plant with two million litres of water storage. We are currently reviewing the design in light of the unprecedented turbidity issues experienced in the recent storm, but once commissioned this new plant will greatly improve the security of our water supply.