Mighty Waikato not an infinite source of water

The sedimentation tanks seperates microorganisms from the water, with the water rising to the top of the tanks and flowing onto the next stage. Photo / Tom Rowland

There is a general idea that if the river is full then Hamiltonians can take as much water as they want from it, however there is more than meets the eye in taking water and turning it into drinkable water for 165,000 people.

Hamilton City Council's compliance manager Trent Fowles said that the biggest constraint for the city is the raw water source.

"We have a resource consent to take water out of the river. Where there is a certain amount we are allowed to take at certain volumes, but part of our consent is to also have a water management plan that shows we are encouraging people to conserve water," Mr Fowles said.

"We're really trying to drive the education of water usage where we can stretch the water to accommodate for new growth, as long as people use it wisely."

Hamilton is currently at water alert level one, which means sprinklers can only be used between 6am and 8am, and 6pm and 8pm, with further levels of restrictions possible if dry weather continues.

It is not just the level of the river that is the main factor for triggering these alerts, but also the river flow levels and the levels of Lake Taupō, which is Hamilton's catchment area.

"There are also restrictions when drought levels and river flows — certain times when the river flow drops — that we have to reduce what we are taking."

The council works closely with Mercury Energy, which operates dams, which also play a part in the river flow.

"Our catchment isn't in Hamilton, but in Taupō, and at the moment the Taupō levels are okay, so alarm bells aren't going at this stage."

"From our perspective, I've been at council for five years (and) we have never had to put anything in place for the river flows. At the same time we have seen Taupō get a little low but have been saved by a bit of rainfall."

Despite this, Hamilton's resource consent allowance is much higher than what the city currently needs, as it takes into account future planning.

"We have our consent limits, but it is not a target for us to get up there.

"The lower the better for us, and we can't store the water for longer than 24 hours so we are not holding back any water. Our consent limits are set for the future so we don't get close to the target right now."

Hamilton's water treatment plant intake is located opposite of the Hamilton Gardens on the south side of Hamilton. Photo / Tom Rowland

Hamilton's sole water source is the Waikato River, and it is treated at the treatment plant in Peacockes Road. The water is then pumped to households and eight reservoirs around the city.

They are Newcastle, Ruakiwi, Hamilton South, Hillcrest, Maeroa, Fairfield, Pukete and Rototuna.

The plant could pull to the city's consent limit, but waters operation manager Adam Donaldson said that would compromise another part of the process.

"While we can pull to our consent limit, we can't treat to it, and that's why we upgrade the plant as we go," Mr Donaldson said. "As the city gets bigger the plant will increase accordingly to manage that but at the moment we are not there."

Currently the plant has a little room before operating at full capacity, but it would cost more money to run the plant at those high levels.

"We're really trying to drive the education of water usage where we can stretch the water to accommodate for new growth, as long as people use it wisely.

"We're constantly upgrading and improving for growth, we could go out and do everything to the plant tomorrow and cater for 10 year's growth, but then ratepayers are paying for that and we don't need it yet."

The plant is about to undergo upgrades to its sand filtration system as part of its masterplan to allow for planned growth.

The barge that can be used to pump water into the Hamilton treatment plant from the river if levels drop below the plant's intake pipes. Photo / Hamilton City Council

Plan B for River intake

* Hamilton's water treatment plant is prepared for the day the Waikato River reaches a level where the water drops below the intake pipes.

* The water treatment plant's only source of water is via a fixed intake structure on the banks of the river, opposite the Hamilton Gardens. Built in the 1970s, this structure requires river flows to be above the intake levels.

* As a plan for this scenario, Hamilton City Council commissioned the construction of a barge in 2016. On board are pumps that are designed to draw water from the river during exceptionally low river levels and into the city's water treatment plant.

* In the case of a drought, the barge will be used to produce the water needed to supply Hamilton.

* While the barge has been tested in the river, it has not been used by council yet.

Water statistics

* On average, each person in Hamilton uses approximately 224 litres of water per day, however in summer this volume can more than double.

* A dripping tap can waste up to 7600 litres of water a year.

* During summer months an estimated 50 to 70 per cent of household water is used outdoors for watering lawns and gardens.

* A garden sprinkler uses over 1000 litres of water per hour.

* Council's water treatment plant is turning more than 2500 glasses of that river water into high quality drinking water which is then supplied to over 50,000 homes and industrial premises. The plant also supplies water to the local fire service.