"It was terrible ... I saw the actual maggots in the water."
Rotorua police are looking into the incident and want to hear from members of the public who could help identify those responsible.
The Health Act carries a specific offence for contaminating water supply which carries a penalty of five years' jail or a fine not exceeding $200,000, or both.
The woman was disgusted, especially since she, her partner and their children had been drinking and using the water. She said the carcasses had been in the tank for at least four days before she noticed the contamination because that was how long the water had tasted "off". However, she said they could have been in there for up to two weeks.
The woman said the tank was covered by a plastic lid which was too heavy for children to lift and a ladder would be needed to gain access.
She now wanted to warn people in her community to check their water tank in case they weren't the only ones targeted. She had heard about poaching happening at nearby farms and thought those responsible for the poaching could also be responsible for contaminating her water tank.
"I think the whole community should be careful.
"This is a real cruel act against children over the Christmas period and I hope they have some conscience."
The woman said since the "malicious act", they have had to reorganise their Christmas plans. She said she was meant to host a big family Christmas and children were meant to arrive this week to stay for the holidays.
Now, she said they would have to pile into her mother's one-bedroom flat for Christmas.
Cleaning the tank is no easy process. She can either pay hundreds of dollars to have it cleaned out or drain, clean and disinfect it herself. At this time of the year, she said she would probably have to do it herself. It would also mean she would have to wait for the rain to refill the tank or have it filled professionally, at even more cost.
Inspector Ed Van Den Broek of the Rotorua police said the woman's report was the only one Rotorua police had received.
"This is a disgusting thing to do to a family's water supply, endangering the health of the adults and children relying upon the water for drinking and other domestic use," Mr Van Den Broek said.
Police would like to hear from anyone who can supply information that will lead to the identification of the offenders. Information can be supplied direct to the Rotorua police on (07) 348 0099, or to Crimestoppers on 0800 555111.