Representatives of Te Rūnanga ō Ngāti Awa are being cross-examined in the Environment Court at Mataatua Marae on the fourth day of hearings.
Te Rūnanga and Sustainable Otakiri are appealing consent for Creswell New Zealand to expand water bottling production at Otakiri Springs.
It was granted consent by the Bay of Plenty Regional Council, and under the proposal would be able to take a billion litres of water annually.
Te Rūnanga ō Ngāti Awa Chief Executive Leonie Simpson says she has serious concerns about the "irreversible" harm to the aquifer.
She told the court the proposed expansion and consents affect the iwi's ability "to be kaitiaki" (guardian) and tangata whenua.
Creswell New Zealand's lawyer, Dave Randal, says it's now agreed that Creswell's proposed take will have a low level effect on the biophysical properties of the aquifer.
But Ms Simpson says that could be seen as a "western Pākehā perspective of how much [water] is there, and is there enough."
She told the court Te Rūnanga is still concerned about the volume of water taken from the aquifer, and the effect on mauri.
Ms Simpson emphasised they are appealing the volume of the take, the water bottling and the export of water from New Zealand, "and our ability to be kaitiaki" (guardian) of the water".
A site visit to Otakiri Springs is planned for later this afternoon, before the court reconvenes at Eastbay Reap in Whakatāne.
Consents should 'be declined'
Ngāti Pikiao has opened its case against the expansion of the water bottling plant.
Its lawyer Rob Enwright says Ngāti Pikiao Environmental Society supports Te Rūnanga's position to decline regional consents.
Creswell New Zealand says its plans to develop Otakiri Springs will create nearly 60 jobs.
However Mr Enwright says Ngāti Pikiao is concerned for health of the aquifer and water take "especially at the volumes involved for the subject proposal".
He says Ngāti Pikiao largely agrees with Te Rūnanga and the outlined effects of the proposal.
It says the proposed water bottling plant will effect spiritual kaitiaki of the water, decision making and planning considerations.
For those reasons Mr Enwright says the regional consents should be declined.
This afternoon Sustainable Otakiri will present its legal submissions.