A three month trial is about to begin to test whether a new treatment system will reduce the impact that algae is having on water filters in Wanaka.

Algae is always present in the lake but Queenstown Lakes District Council’s Chief Engineer, Ulrich Glasner, says most people would not be aware of it unless they had appliances with filters that were clogging up. The problem always gets worse over summer, partly because algal growth increases in hot weather, and partly because of the dramatic spike in water use. The algae is present in both of the Council’s water supply intakes, at Beacon Point and Rippon.

The algae is invisible to the naked eye, tasteless and, according to laboratory testing, is not harmful to human health, Mr Glasner says. However, because of the inconvenience to householders who have to clean the filters on their appliances, the Council has been investigating ways of reducing its impact. The algae is also affecting water meters installed in sample properties as part of the Council’s ongoing water use study.

The algae has been extensively investigated and monitored over the years to ensure there was no impact on human health. Several options have been considered to deal with the algae, with one that looked particularly promising unfortunately proving to be prohibitively expensive. Whatever solution is found will have to be installed at both the water supply intakes.

The latest trial involves technology developed by Veolia, used extensively in Australia and most recently trialled in Thames Coromandel. The plant is being installed this week and will be commissioned by the end of the month.

The plant is expected to process 240,000 litres of water a day and Mr Glasner says the results will be monitored to assess its effectiveness in removing the algae. While that might sound a large amount of water, it was only a fraction of the 22 million litres of water going through the Wanaka water supply at the moment. Most of that water was being used for irrigation because of the prolonged dry weather.

The Council has budgeted $319,000 this year for Stage 1 of a new borefield near the Wanaka Yacht Club, which will provide water to the CBD and reduce the pressure on the two existing reservoirs. Water from the new bore would not be affected by algae as it would not be coming directly from the lake.

Fast facts:

• The plant being trialled is an Actiflo Mini pilot system developed by Veolia.
• It will process the water, which will be monitored to check algae levels, and the water will then be pumped into the Beacon Point reservoir
• Algae removed in the process will be pumped into a purpose-built sludge tank
• The trial will last for 90 days, after which its effectiveness will be assessed.