Which size water tank do you need?

Calculating the size of a rainwater harvesting tank involves considering several factors, such as the average rainfall in your area, the surface area available for collecting rainwater, the intended use of the harvested water, and any specific requirements you may have. Here’s a general approach to help you calculate the tank size:

1. Determine your water needs: Start by assessing how much water you need to store. Consider your household or specific usage requirements, such as gardening, irrigation, or toilet flushing. Calculate the average daily water consumption or the amount of water you want to collect during a specific period.

2. Determine the collection area: Next, determine the surface area available for collecting rainwater. This could be the roof area of your house, a garage, or any other structure that can efficiently capture rainfall.  Measure the length and width of the collection area and multiply them to get the total collection area in square meters.

3. Determine the rainfall factor: Research the average rainfall in your area. You can obtain this information from local weather records or online databases such as the Met Office. The rainfall is usually measured in millimeters. Convert the rainfall value to the same unit as your collection area (e.g., millimeters to square meters).

4. Calculate the volume of water: Multiply the collection area by the rainfall factor to determine the volume of water that can be collected during a rain event. This will give you the amount of water in cubic meters.

5. Consider efficiency and storage capacity: Rainwater harvesting systems are not 100% efficient  due to factors like evaporation, leaks, and system losses. To account for these inefficiencies, multiply the calculated volume of water by a factor between 0.5 and 0.9. This will give you an estimate of the effective volume of water you can expect to collect and store.

6. Calculate the amount of persons or animals usage

7. Select the tank size: Based on the effective volume of water calculated in the previous step, choose a tank size that can accommodate that amount. Rainwater tanks are available in various sizes and shapes.

Consider factors like available space, budget, and any local regulations or restrictions on tank sizes.  It’s important to note that this is a general approach to help you estimate the tank size. You may need to adjust the calculations based on specific factors in your situation. Additionally, it’s recommended to consult with local experts or rainwater harvesting professionals who can provide more accurate guidance based on your location and specific needs.