Water use at the three sites, especially Lower Penns, has been repeatedly discussed at recent society meetings.
The society heard that this year's dry weather has seen water use increase, with one quarterly bill for Lower Penns now at least £30 higher than the same time last year.
The August meeting briefly discussed raising rents to cover the costs.
The society heard that rents have not been increased since the society took over managing the plots two to three years ago.
Water use and costs will continue to be monitored and rents for next year will be set at the October meeting.