Water Capture and storage – financial benefits
The financial benefits likely from installing one’s own rainfall water capture and storage system.
We consistently recommend that all households who can afford it should install the most appropriately sized household water tank system that they can afford.
But how does one go about calculating the best options? We recommend proceed as follows:
- Decide your own goals; e.g. financial savings, water security, water availability convenience, unlimited gardening, and so on.
- Calculate different alternative systems for your household roof size to see which makes the most sense in terms of your goals; calculate the appropriate sized system using the Water Research Commission WRC CSAG Water Harvesting Tool here. When using this model to calculate different combinations, it should become clear that the smaller the roof area the smaller the optimum tank size becomes. In other words, little savings benefit is gained from spending more on a relatively oversized tank.
- Using the WRC calculation tool, note the amount of water that will still need to be drawn from the municipality each month. Using the City of Cape Town published tariffs (read them here), calculate what this remaining water purchase will cost each year.
- Following the model below, then determine the approximate costs of your preferred option and calculate your likely annual water and sewerage costs both before and after implementing such a water harvesting and tank storage system to complete the comparison.
Financially, what will the cost of an appropriate tank installation be? How long will it take to recover the capital? What would subsequent savings be over the life of the installation?
Here are three examples drawn up using the UCT WSC model to estimate water harvested and of the remaining water therefore still needing to be drawn off municipal supply, assuming houses of different roof areas located in Pinelands, and the installation of two different tank sizes – 2000L and 5000L.
Cost calculations will obviously vary depending upon how the installation is made and the material used. The following costs are approximate assuming a D-I-Y installation.
This shows 3 outcomes for a hypothetical family of four using 12,000 litres of water each month.
Assuming that the tariffs implemented 1st June 2017 apply throughout, then the capital cost is paid back between 2.8 years and 4.1 years. Additional savings achieved over the remaining part of an assumed 20-year lifetime of the installation are also shown.
[Financially adept readers will recognise that these calculations may be refined by applying accurate time-cost of money, cost escalations, write-off provisions and the like. My intention was to keep this example simple just to illustrate a point. I leave the further calculation refinement to you].When one takes into account all the very tangible advantages of creating one’s own water storage as well as the intangible benefits provided by attaining water security, then the decision appears to become very straight-froward.