Buried watering from a tank is a recurrent question on our forum, and Nicolas, our watering specialist, brings us his analysis of the question.
"Automatic watering of a lawn from a rainwater collection tank is more of a philosophical choice than an economic one."
Example:
- You install a 6500 liters tank (2000 Euros or the equivalent of 500 000 liters of "drinking" water)
- You install an automatic watering pump, thus automated with its various safeties (500 Euros, i.e. 125 000 litres of water)
=> You must therefore consume 625 000 litres of water before you can amortize the installation (we'll skip the "various and sundry" costs that come on top of this, including the earthwork and the masonry installation for a tank, the overflow drain, the supply through the gutters, the installation and the wiring of the pump... )
After 625 000 liters of water, we begin to earn money (once again, I pass the maintenance of the installation, wear of the pump, or simply the electric consumption of a pump which must function 250 hours at best for this flow, for a motor of 1000 Watt).
325,000 liters = 156,000 m² of lawn for information.
=> Assuming that you have 1000 m² of land, you need -only- 150 days of watering to amortize the installation. But the problem is that during these 150 days of watering, there is no water in the tank. A (full!) tank of 6500 liters can automatically water 1500 m² of lawn, but the next day the tank is empty...
The use of a tank with its pump, its installation and its maintenance is rather expensive and it takes years before it is amortized, it can't be a financial choice (to save money), it's much cheaper to pay city water, especially in the short and medium term. Especially since it is possible for large plots of land to have water half as expensive by the water company (that's another subject).
A tank, even a big one, does not allow to do the underground watering of an automatic installation. A tank allows you to water your vegetable garden, to water your window boxes, to let your children play with water, to wash your car (a little), from time to time. It is a product that is often empty when you need it, and that overflows when it is winter...
The tank filled with rainwater is not a product suitable for automatic in-ground watering of the lawn unless you have a tank with a much larger reserve.
