Equivalent Tenements Explained
It is not practical or cost-effective to install, maintain and read sewage meters on each property that we service, so we estimate the load and the cost to attribute to each property. Utilities around Australia estimate the sewage load that properties place on their networks in different ways. We use an Equivalent Tenement (ET) method to calculate sewerage prices.
One ET is the estimated load of sewage from an average residential house in dry weather flow conditions. It is a proportion of a water ET, on the basis that a proportion of ‘water in’ will appear as ‘water out’. ET sewage rates for different land uses are calculated as a factor of this load. For example, where the use of a property has the potential to result in sewage flows four times as much as that of one residential property, it will be assessed as four ETs and will pay four times the sewerage charge of a residential property.
Our ET approach is based on Section 64 of the Determination of Equivalent Tenements Guideline of the NSW Water Directorate. The ETs from the Guideline have been adjusted for Tasmanian conditions, to reduce administrative complexity, increase fairness or to respond to customer concerns. Supplements are the WSAA Sewerage Code of Australia: Part 1 and the TasWater Supplement to the WSAA Gravity Sewerage Code of Australia.
Water ETs are based on actual average water use. An assumed discharge factor is applied to arrive at a sewage ET. For one sewage ET, the assumed areas of water use in a house are set out below:
- Kitchen – 15 per cent
- Laundry – 25 per cent
- Toilet – 30 per cent
- Bathroom – 30 per cent.
For the PSP4 period, we have made a number of refinements to improve the fairness and accuracy of our ET approach, including:
- Combining some ET categories to reduce complexity
- Updating ET unit measures to more accurately reflect load on the system
- Refining categories and ET units for customers who also pay trade waste charges.