System setup

Assessing Performance of Different Sized Rainwater Storage Tanks

The performance assessment of various sized storages involves the calculation of the amount of water in storage for a given day. This calculation is based on the water balance shown above. This is a simple calculation, however, using a computer allows this calculation to be completed for many consecutive days of rainfall data. This is equivalent to trial sizing a storage tank size over the period of assessment (over many years).

The computer model completes daily water balance calculations, so that any roof runoff generated from rainfall in that day is calculated. The computer model also calculates the daily level status of the water storage used to hold this rainwater.

During any one day the storage could overflow depending on the amount of roof runoff generated. Likewise, the storage could also be emptied if the volume of water used exceeds the amount of water available from the storage. In this case, water must be supplied from other sources in order to fulfil the water demand. The computer model calculates and sums the amount of water supplied from other sources over the period of assessment. This information can then be used for a comparative assessment of the different amounts of makeup needed with use of different size water storages.

Rainwater harvesting systems can range in complexity, from systems that can be installed with minimal skills, to automated systems that require advanced setup and installation. Systems are ideally sized to meet the water demand throughout the dry season since it must be big enough to support daily water consumption. Specifically, the rainfall capturing area such as a building roof must be large enough to maintain adequate flow. The water storage tank size should be large enough to contain the captured water.\

For low-tech systems, there are many low-tech methods used to capture rainwater: rooftop systems, surface water capture, and pumping the rainwater that has already soaked into the ground or captured in reservoirs and storing it into tanks (cisterns).

Before a rainwater harvesting system is built, it's helpful to use digital tools. For instance, if you want to detect if a region has a high rainwater harvesting potential,rainwater harvesting GIS maps can be made using an online to. Or if you need to estimate how much water is needed to fulfill a community's water needs, the Rain is Gain tool helps with this. Tools like these can save time and money before a commitment to build a system is undertaken, in addition to making the project sustainable and last a long time.