An ageing treatment plant is struggling to provide Northland's busiest tourist town with sufficient drinking water in the face of floods, silt, varying raw water quality and increasing demand.

Treated water for Paihia, Waitangi and Haruru comes from the Waitangi River, just upstream from Haruru Falls.

According to a report presented to a recent meeting of the Far North District Council's infrastructure committee, the treatment plant, which is next to the Haruru Falls bridge, faces a raft of problems. Each problem could be solved on its own but together they mean the plant is nearing the end of its useful life.

Paihia's water treatment plant is upstream from Haruru Falls, on the Waitangi River just beyond the bridge. Photo / file
Paihia's water treatment plant is upstream from Haruru Falls, on the Waitangi River just beyond the bridge. Photo / file

With no capacity for raw water storage the plant has to process whatever water is in the river at the time. During storms high levels of silt can drastically reduce the plant's output or force it to shut down. This also happened in 2011 when a resident about 1km upstream illegally diverted the river.

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The lack of storage also means any pollution event upstream would force the plant to close until the risk had passed.

The plant's confined site — it is hemmed in by the river, private properties and a road bridge — means expansion or improvement, such as adding raw water storage or even making it comply with new laws around storing hazardous chemicals, is not possible.

The report also stated the council fielded regular complaints about water taste and odour. Problems in the summer of 2017-18 were due to geosmin, an organic compound created by river microbes, which can cause a strong earthy taste at levels as low as 10 parts per trillion. Levels at that time reached 59 parts per trillion.

The report added that the plant's location made it vulnerable to flooding, with two floods in 2007 entering the building and causing electrical damage.

Demand for water in mid-summer in Paihia now exceeds the plant's capacity, but the report noted the town also had a high level of ''unaccounted for water'' — in other words, leaks in its water pipes. Finding and fixing those leaks would give the council more headroom to deal with summer water demand.

The council has been granted $353,000 from the Government's Tourism Infrastructure Fund to carry out sewerage and water treatment feasibility studies for Opua, Paihia and Waitangi. The fund supports local authorities which have a small ratepayer base but large numbers of tourists.

The council's 2018-28 Long Term Plan has set aside $6.8 million for a new water treatment plant, with the funding earmarked for 2021/22 and 2022/23. Report author Barry Somers, however, said the actual cost was likely to be higher.

Paihia's ageing water treatment plant is only one of many infrastructure challenges facing the Far North District Council. After legal action by the Northland Regional Council earlier this year it was forced to spend $6m upgrading the town's outdated sewage treatment plant.

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Sewage plants in Hokianga also regularly breach their consent conditions, and it was revealed last week that Kaitaia's water reticulation system is plagued with leaks.