Wellington residents say the Prince of Wales Reservoir would be like having the second coming of Noah bearing over them.
The 35 million litre concrete reservoir would provide portable water for 70,000 residents, commercial and industrial businesses and critical community facilities.
Wellington city councillors are scheduled to consider granting an easement for the work on part of Mt Cook's Town Belt this morning.
The project is yet to gain resource consent.
Council officers said in a report there were several walking tracks across the site including the City to Sea and a mixture of grassland, gorse and generating native shrubs.
"The effects on Town Belt values during construction of the proposed reservoir will be significant and adverse but will be outweighed by the longer term community benefits".
Mt Cook Mobilised chairman Peter Cooke said those living on Rolleston and Hargreaves Streets would be most affected by construction work.
He said residents were concerned about dust, noise, trucks going up and down the streets and the reservoir itself.
"The tank will basically be at the top end of those two streets so some residents are concerned about their safety if the tank were to rupture, they fear a great big flood of water, the second coming of Noah."
Cooke said residents were also concerned about two playing fields which would get messy during the reservoir's construction.
"We would certainly expect them to be put back into service in a better condition than they are now, both of them get rather boggy in Winter."
Wellington Water spokesman Alex van Paassen said there was a proposal to raise the level of the fields by up to 1.5 metres to reduce the amount of excess soil being carted away.
He said if the proposal went ahead, it would halve the more than 5,000 truck loads needed to remove the earth from the reservoir site.
"The engineering for retaining any soil used to increase the height, improve the drainage and level out those playing fields would be absolutely secure."
The fields could be out of action for three years.
Council officers said the fields were used for sports like rugby, cricket and football but they were confident there were other locations in the city to accommodate the teams.
They said Wellington Water would be required to leave the fields in a better condition whether the excess soil would be used to raise the level of them or not.
Van Paassen said the reservoir was built to be resilient because the whole point of it was to be Wellington's back up water supply in the event of a natural disaster.
"If there was an event such that this reservoir were to fail, I don't think that there'd be a lot of people around to worry about the water coming down the hill.
"It would just have to be of such a scale that the other impacts of something like an earthquake would be much more significant than the possible cracking of the reservoir."
He said Wellington Water would continue working with concerned residents.