District council water services team leader Cinnil Thomas said all land developers working within the district council area are registered and are authorised to take water.
Companies are charged $0.44 per 1000L.
Extractions are detected by the district council's online systems.
The district council will also use media campaigns to dissuade people from engaging in illegal extraction.
But Thomas said like other council areas, there are sporadic instances of unauthorised extraction of water in Selwyn.
"The district council is working on a process framework for extraction of water by entities other than land developers," she said.
The Rolleston resident said if other people knew about the issue, residents can try and get these companies held to account.
"Tankers can pull up and nobody notices them much and they skulk off with all our water we are paying for," the resident said.
She said it irked her tankers were pulling up and taking water with no restrictions and she often saw litres of water spilt over the ground.
"I don't want to see a tanker right next to my meter taking thousands of litres for free while I am paying for every litre I use," the resident said.
If residents see companies taking water, they can email water.services@selwyn.govt.nz
Meanwhile, there is no immediate need for mandatory water restrictions.
However, the district council is asking residents to consider changing the lawn irrigation timing to keep water networks
stable.
Thomas said water supplies are placed under pressure during summer as many people decide to water their lawns and gardens at the same time.
