Whangārei council to use treated wastewater to irrigate gardens and sports fields

Whangārei District Council will start using treated effluent from the city's main wastewater treatment plant to irrigate gardens this week. Photo / Michael Cunningham

Whangārei District's residents have been saving shower and dishwater to keep their gardens green, reducing the water use by 18.2 per cent – and now the council's parks and recreation team will be doing a similar thing on a grander scale.

Whangārei District Council will start using treated effluent from the city's main wastewater treatment plant to water trees, sports fields under renovation and garden beds when water restrictions are in place.

A resource consent, granted by the Northland Regional Council in consultation with the Northland District Health Board, set up a permanent system that can be used during water restrictions now and in future years without having to apply for new consents.

"Even though we have had a little rain, the ground is still extremely dry. Many of our trees have taken decades to grow, and they really need deep watering," parks and recreation manager Sue Hodge said.

"We also make a big investment in fields every year. They are very important to the community, especially with the winter sports season coming up and we want to look after them as well as we can."

The consent rules are strict to ensure the water is low in bacteria, has been ultraviolet treated and is dosed with chlorine as an extra safety measure.

The water cannot exceed 1000 cfu (colony-forming unit) per 100 millilitres of faecal coliforms and can be used to only water garden beds, trees and sports fields.

Council can't use the wastewater irrigation within 20 metres of any property, 15 metres of the coastal area or freshwater sources, or five metres of stormwater flow paths.

There are no known groundwater bores near any of the proposed irrigation areas.

"We expect that it will smell, compared to fresh, potable water, so there are restrictions around its use to ensure that odour is managed along with health and environmental protection," Hodge said.

"We will be closing the fields after each watering until the ground is dry, as an extra precautionary measure."

Council consulted with NDHB on the potential effects on human health. It confirmed that the treated wastewater irrigation should not adversely affect people – this is provided the treated wastewater is not irrigated on active sports fields and that council puts up appropriate signs.

Gavin de Klerk, NDHB's healthy environments team leader, confirmed the consent had taken into account the parameters the Ngā Tai Ora Public Health Northland requested to ensure public health is protected.

Despite rainfall over the past week, water restrictions Level 2 are still in place across the district with Level 3 restrictions remaining a possibility.

WDC spokeswoman Ann Midson said while Whau Valley Dam volume decreased by only 1 per cent and residents made a great effort in conserving water, further restrictions were still within the scope.

"We haven't scheduled any new restrictions yet, but Level 3 restrictions remain a real possibility unless we get substantial rain."

Midson said the rainfall over the past days didn't refill the dams and other groundwater resources "in any measurable way" and only made a "cosmetic difference" to gardens and green areas.

A low-pressure system travelling north over the country brought some showers to Northland yesterday.

MetService meteorologist Andrew James said the forecast for the coming days was mostly fine with some isolated showers.

On Friday, a subtropical low is expected to approach the North Island bringing strong easterlies over the upper North Island ahead of the low.

James said the low might bring more rain over the weekend, but it was too early to confirm.