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Rainwater Harvesting: an alternative for water scarcity

A recent study about the global rainwater harvesting market shows that larger systems will demand higher maintenance than domestic ones.

No wonder water is one of the most precious sources in the planet. The United Nations (UN) estimates that there will be around 2-3 billion people living in areas of water stress by 2025. That would amount up to 37% of 8.2 billion people, or more than a third of the Earth's population estimated by 2025, according to the UN.

Accordingly, there are neither few nor recent diversification efforts for the precious resource, as well as solutions for more efficient uses. One of the most basic and ancient forms is rainwater harvesting. Spread in drought periods as an alternative to domestic use, from the economic point of view, harvesting is not a universal solution, as common sense implies. However, it is one of the most important options when dealing with water stress, such as the one predicted for the next decades. This is highlighted in a recent study of BCC Research, an expert consultancy on market research. According to the study, the global market for water reuse is expected to grow 5.3% between 2017 and 2022, when it will be worth an estimated US$1.5 billion.

“Rainwater harvesting is an easy and affordable solution to overcome such water stress and it acts as an important alternative as a decentralized water source. This type of alternative water source also helps in reducing the use of fresh water from surface and groundwater sources”, said Srinivasa Rajaram, analyst and report author of BCC Research. He points out that rainwater storage and reuse can protect sanitation structure of the cities.

In times of heavy rains - when a full month's rainfall falls on a single day, as it is increasingly seen - rainwater reuse systems help to reduce stress in rainfall infrastructure. Instead of rainwater going to galleries and overloading streams and rivers, it is kept in the water tanks of reuse systems. This means less flooding, which, in turn, reduces municipal expenditures not only with infrastructure, but also with health and transportation, among others. Harvesting and reusing with restrictions Not everyone sees reusing rainwater the same way Rajaram does.

Harvesting and reusing with restrictions

Not everyone sees reusing rainwater the same way Rajaram does.

José Carlos Mierzwa, teacher in the Hydraulic and Environmental Engineering Department at the Polytechnic School of the University of São Paulo and one of the founders of the International Reference Center for Water Reuse (Cirra - Centro Internacional de Referência em Reúso de Água), acknowledges the importance of the technique, but points to some limitations. For starters, he says, this is not a solution for everyone, and also, there are better options for homes or commercial buildings with smaller harvesting areas - usually installed on slabs or roofs.

"Sometimes, you can reduce [rainwater] consumption by installing equipment [such as flow reducers], which save more than a rainwater harvesting system", claims the expert. "In some cases, investment and maintenance for the [rainwater harvesting] system may not have as much benefits as the return it brings", he explains. Also according to Mierzwa, a survey of BCC Research, somehow, indicates this. The rainwater harvesting equipment industry sold US$ 1.1 million in 2017, and it is expected to reach US$ 1.3 million by 2022. "It's not much if we consider we're talking about a global report", he says.

The market for rainwater reuse currently has two segments: the sale of basic harvesting equipment and the assembly, commissioning, service and maintenance of this equipment. It is not enough to install the rainwater harvesting system; it must be monitored to avoid losses and leaks. The maintenance and planning segment is expected to increase 6.2% per year by 2022 and close this cycle with an annual revenue of US$ 205 million. "But there are a lot of people who do not even think about how much they could reduce their own [rain] water consumption thanks to a rainwater harvesting system," says the professor.

For Mierzwa, rainwater reuse is worthy, mainly, for large commercial and industrial operations, which consume equally large volumes of the resource in its distribution network. "For shopping centers and industries with large slabs, the installation of a rainwater harvesting system pays off quickly because it replaces a paid source with a virtually free one," Mierzwa explains. For him, outside of big centers, the solution is economically feasible only in regions with serious water scarcity. "In Brazil, this would be the case of the Northeastern semi-arid region, of a place like Northern Minas Gerais or a remote community whose population is not served by a supply system," he says.


In the United States, where droughts are getting worse each year, there are many incentives for adopting rainwater harvesting systems. In Arizona, Southwest of the country, those installing such systems are entitled to a one-time tax credit of 25% on the amount invested to offset installation costs. In California, deeply affected by the drought in recent years, there are tax incentives for backyard facilities, as well as a proposal to rule out rainwater reuse systems from the property taxes. In Santa Fe, New Mexico, lawmakers have been bolder: every new property is legally required to have a rainwater harvesting system.

Rainwater can also be an alternative to agriculture, especially in drought regions. However, adopting an efficient solution requires great investment, since the volumes required are larger, and storing them is more costly and complicated. Currently, the dams are the most recommended option. "The system works best when it is used to irrigate what has the biggest economic value," says Mierzwa. "Vegetable production is a good example, since it is a profitable crop with a shorter cycle," explains Mierzwa.

Nevertheless, in large cities, Mierzwa is more skeptical about the positive effects of a rainwater reuse system. According to him, in some cases, the best alternative is to invest in broader measures, such as drainage and pollution control of water sources. Considering the investment return, rainwater harvesting is not an advantage over integrated systems such as water reuse from sewage treatment. Still, and despite criticism of domestic use, Mierzwa believes that rainwater harvesting will remain in major water-scarce regions. 

What can you do?
CMHC, Canada Mortgage and Housing Corporation, was created to assist Canadians in housing issues, and has produced rich materials on rainwater harvesting and reuse systems. Operational information, tips and quotes are freely available online.

O que a Braskem
está fazendo
sobre isso?
Braskem is present in several fields of the rainwater management, storage and reuse system. Most of the water tanks used in these systems have polyethylene in their composition. Low-cost, compact-size cisterns also use plastic ostensibly. The high-strength PVC used in rain gutters that take rainwater to the tanks are often manufactured with Braskem's inputs.