Rainwater harvesting makes it possible to transform part of that rainfall into a useful resource. Depending on the characteristics of the site, the water can be stored for specific uses, directed toward crop areas, or allowed to infiltrate the ground.
What is rainwater harvesting?
Rainwater harvesting involves collecting, channeling, and utilizing water from precipitation before it leaves a home, lot, or property.
The simplest example is rainwater falling on a roof. Through gutters and downspouts, it can be channeled to a tank where it will be stored for later use. But there are many more possibilities.
It is also possible to capture water from roads, patios, and other surfaces, as well as to make direct changes to the landscape to slow runoff and allow more rainwater to infiltrate the soil.
That is why we can distinguish between two main methods of water management: storing water in infrastructure or storing it within the landscape itself through infiltration. In many projects, these two strategies can complement each other.
How much rainwater can be collected?
Before installing any system, it is a good idea to have a rough idea of how much water we can collect. The potential depends mainly on two factors: the available surface area and the local precipitation.
As a simple reference, 1 millimeter of rain falling on 1 square meter is roughly equivalent to 1 liter of water, before accounting for losses. This means that a 100-square-meter roof can collect approximately 5,000 liters during a cumulative rainfall of 50 mm.
Not all of that amount will necessarily reach the storage tank. There are losses associated with the system itself, such as evaporation, initial runoff, dirt, or overflows. Even so, performing this calculation helps you understand the potential of a home or property and better size the system. Installing a tank without analyzing this data can lead to two opposite outcomes: having much more capacity than necessary, or having a tank that fills up immediately and wastes a large portion of the rainfall.
Rainwater Harvesting from Roofs
Roofs are one of the easiest surfaces for collecting water. Rain falls on a relatively clean surface, is channeled through gutters, and can be easily directed to a storage location.
A basic system may consist of a collection surface, gutters, downspouts, filtration components, a system for managing initial runoff, and a storage tank. However, the design will ultimately depend on the intended use.
Collecting water to water a small garden is not the same as seeking greater water self-sufficiency for a home or having a reserve for a productive farm. The roofing materials and potential sources of contamination must also be taken into account before deciding how the collected water can be used.
Rainwater Storage
Once the water has been collected, the next step is to decide where to store it. Storage tanks can be installed above ground, buried, or integrated into various types of infrastructure. Their capacity should be determined based on rainfall, the catchment area, available space, and, most importantly, projected consumption.
A reservoir that is too small may fill up during the first rains and subsequently lose much of its available water through the spillway.
On the other hand, installing a large storage capacity does not always make sense if the catchment area or precipitation levels are insufficient to fill it. The goal should be to strike a balance between available water, catchment capacity, and actual needs.
What can the collected water be used for?
Possible uses depend on the system installed, the quality of the water obtained, and applicable regulations. One of the most common uses is for watering gardens, vegetable gardens, trees, and agricultural areas.
Certain non-potable domestic uses may also be considered if the system is specifically designed for that purpose and meets the relevant requirements. On a property, the stored water can also help reduce dependence on other sources during certain times of the year.
The key is to define the objectives from the start. Knowing how we intend to use the water allows us to calculate our needs, select the appropriate storage solution, and properly design the entire system from the intake point to the point of use.
Rainwater Harvesting on a Farm
When we think of a house, we usually think of the roof first. On a property, however, the possibilities are much greater. Rain falls over the entire surface of the land and then begins to flow down the slope.
This movement can cause runoff, erosion, and soil loss, but it also presents an opportunity to manage water differently. A good strategy can identify the areas through which water flows, slow its speed, and direct part of the flow to places where it can be stored or infiltrate the ground. Roads, compacted areas, slopes, and even certain infrastructure can serve as catchment areas.
Thus, rainwater harvesting on a property is not limited to installing tanks; it can be part of a comprehensive hydrological design of the landscape.
Water Infiltration: Storing Rainwater in the Ground
A reservoir isn’t the only place where we can store water. The soil also acts as a massive reservoir. When we allow more rainwater to infiltrate, we increase the moisture available to trees, crops, and vegetation. To achieve this, various strategies can be used depending on the characteristics of the terrain: infiltration zones, interventions along contour lines, revegetation, small retention structures, or measures designed to reduce runoff velocity.
The idea is to keep water on the property longer. Instead of trying to quickly drain away every rainfall event, we can analyze where it would be beneficial to slow down, distribute, and infiltrate the water.
Reservoirs, retention basins, and infiltration: there is no single solution
One common mistake is to look for a single infrastructure capable of handling all aspects of water management. In reality, a property can benefit from different solutions working together.
Some of the rainwater running off the roofs can be stored in tanks. The excess can then be directed to an infiltration area. In another part of the property, it may be worthwhile to create a retention pond, while certain paths can be designed to channel water toward vegetated areas.
This creates a system in which water can be reused several times before finally leaving the property.
The right solution will always depend on the terrain and the project’s objectives.
At La Casa Integral, hydrological design and consulting make it possible to study the characteristics of homes, lots, and properties in order to develop water collection, storage, and infiltration strategies tailored to each location.