Building

Adapt buildings for rainwater harvesting

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Objectives

• Use of free water / saving tap water
• Energy savings from processing water at scale

Green Value indicator

• Water footprint
• Helps manage stormwater run-off to prevent erosion, flooding and poor water quality in our lakes and streas.
• Municipal water treatment and pumping require energy and chemicals. Rainwater systems reduce this environmental cot.

Explanation

The main reason for harvesting rainwater is to provide an alternative source of water to buildings and other installations. Thus, the adoption of this system allows to capture, divert, and store rainwater from rooftops for later use: washing, topping up a cooling tower, and toilet and urinal flushing, watering plants.

And it is also possible, with additional filtration and disinfection, to improve harvested rainwater to human consumption standards to supplement municipal drinking water.
Therefore, rainwater harvesting contributes to reducing the consumption of water from the municipal water supply or generally minimizes the demand for processed water (less water will be extracted from sources such as dams, rivers, seas, and oceans). Rainwater harvesting also enhances water sustainability by saving energy that is used in the extraction, processing, transportation and pumping of water.

According to Almeida et al., (2021), the process of rainwater harvesting is based on the collection, storing, treatment (sometimes) and use of rainwater from an impervious area, generally from rooftops.
The possibility to construct rainwater harvesting systems varies locally and relies on several factors (socio-environmental conditions, climate pattern, water treatment method, and even availability of construction materials). Large buildings (e.g., universities, companies, public buildings.), have different water consumption profiles and, in general, higher water needs. In this sense, the catchment area and tank sizing must be prudently designed in accordance with the specific characteristics of use and occupancy of each building (Almeida et al., 2021).

PROS/CONS of the action

Pros:

• Municipal water treatment and pumping require energy and chemicals. Rainwater harvesting systems reduce this environmental cost.
• The use of rainwater treatment decreases the need for tap water.
• The implementation of rainwater harvesting systems not only conserves water but also alleviates stormwater runoff.
• It is possible to combine rainwater treatment with other nature-based solutions, namely green roofs, which provide other several economic and socio-environmental benefits, improving urban environmental quality. In higher rainfall regimes, combined systems could be positive, because green roof solutions provide some attenuation and delay of peak runoff as well as stormwater runoff volume reduction.

Cons:

• Green roofs and rainwater harvesting when combined present some characteristics that are still little studied, and the results obtained are not conclusive for Mediterranean conditions.
• The combined systems (rainwater harvesting + green roofs) would be unfavorable in low rainfall regimes, since it would reduce the volume of rainwater collected and stored, thereby decreasing the harvesting efficiency.

Certified

Not Certified

Link to useful sources

Almeida, A. P., Liberalesso, T., Silva, C. M., & Sousa, V. (2021). Dynamic modelling of rainwater harvesting with green roofs in university buildings. Journal of Cleaner Production, 127655.

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Office of Energy Efficiency & Renewable Energy, Water-Efficient Technology Opportunity: Rainwater Harvesting Systems. Retrieved from: https://www.energy.gov

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