Tauranga City Council wants rural Oropi Road in the Western Bay of Plenty District tar sealed to keep the city's water supply clean.

Council reports approved this week reveal sediment from the road is polluting the city's microfiltration plants, which take their water from the Tautau and Waiorohi Streams for the city's 114,000 inhabitants.

Where Tauranga's water is being polluted.

Operating costs are increasing by $583,000 each year dealing with the ongoing problem and increased sediment in both streams during heavy rain has caused both plants to be shut down - a measure that protects the plants but increases the public health risk.

The city council recently spent $3.6million on the plant to pre-treat Waiorohi Stream water prior to processing at the Oropi plant.

The silt is coming from both Oropi Road and the Oropi Gorge Road.

The Tautau stream is collecting silt from the unsealed portion of Oropi Road that crosses the stream.

The Waiorohi Stream is being polluted by slips on unstable road side banks, following road widening work undertaken by the WBOP District Council in Oropi Gorge Road in 2009.

Tauranga residents have been drinking Tautau stream water since the late 1950s.

But the political landscape has changed since then with the issue now the responsibility of all three councils; Tauranga City, the Western BOP District, and the BOP Regional Council.

In a three-cornered process the city, district, and regional councils are submitting on the regional and district councils' long term plans for funding to seal the road.

The city council submissions were approved at Tuesday's Strategy and Policy Committee meeting.

Tauranga City and BOP Regional councils are submitting to the Western BOP District council for $600,000 to be included in the long term plan for sealing 2km of Oropi Road where it crosses the Tautau Stream.

The city and district councils are submitting to the regional council's long term plan for $300,000 of regional council money to be allocated to the district council for the work, as a contingency if the money does not appear in the district long term plan.

The reports states this is because the road does not carry enough traffic to trigger action by the council.

The report also states WBOPDC breached the requirements of the regional water plan and the land plan.

The unnamed consultants overseeing the gorge road widening work did not apply for a consent. The regional council staff say a consent was required – plus a thorough geotechnical investigation.

The district council has a responsibility to address the issue under the Resource Management Act 1991, and the Regional Water and Land Plan.

The city council has a responsibility to promote water quality as a water supplier under the 69U of the Health Amendment Act 2007.

The regional council is involved under the National Environmental Standard for Sources of Drinking Water.

By law it is obliged to ensure consents are not granted for a discharge into a water supply catchment that would cause water (after treatment) to fail drinking water standards.

Samples of run-off from the roads exceed the limits set in the BOP Regional Water and Land Plan.

The Aqua Terra consultant's report on the issue says enforcement action may have to be taken by the regional council if results are not achieved in a timely manner.