There are those in vehement denial of the research and data indicating that water resources across the planet are growing increasingly scarce. For others, it's abundantly clear: Climate change, overdevelopment and population growth are leading to severe shortages of potable water.

Major urban centers around the world are being affected, including Perth, Australia, and Cape Town, South Africa. Lately, Cape Town's city officials have forecast a shutoff of the city's taps within a period of several months — as a means of rationing what scarce water is left in the drought-stricken city's supply among the growing, restless and increasingly desperate populace.

In this challenging environment, the American Society of Landscape Architects, in a recent post, reminds readers that rainwater harvesting is an important tool. Not only as a centuries-old salve, but as one souped-up by current ancillary technologies. Rainwater harvesting (RWH) began as "an efficient sustainable water management technique common before public utility departments centralized and then redistributed water."

According to Texas A&M University's Agrilife Extension website, RWH's main benefits include:

  • less consumption of a locality's distributed potable water, since as much as half a home's total average water consumption is devoted to landscape irrigation
  • reduced overall demand on the existing water supply and hence lower water bills
  • otherwise better management of rainwater as a resource to be conserved

In step with what remains a slowly developing and enveloping crisis, city and state building codes — domestically and internationally increasingly include regulations for RWH. Indeed, many of them aren't so much restrictions on RWH as they are rebates and inducements designed to encourage it — for example, some of California's recent proposed laws, generated via the statewide initiative process and enactable by statewide ballot.

Likewise, RWH as a science is enjoying continuing advances in the design, modeling and implementation of such sustainable systems. RWH can be any system that diverts, gathers and stores falling rain. A roof, existing or newly built, by definition a water drainage device, is typically the starting point. But RWH can also start with any impervious-to-water surface, such as a terrace, courtyard or highway.

Not surprisingly, RWH systems are more characteristic of suburban and residential regions versus more pastoral and rural ones (since many more roofs are present in the former). To such roofs, RWH adds devices that refine direction, collection, diversion and storage of water. Most often, the water is funneled from the gutters into a catchment tank, in the form of a barrel, a subterranean cistern or a superterranean tower.

The rewards for the building owner or homeowner are ample. For example, landing upon a 1,000-square-foot roof, an inch of rainfall can produce 600 gallons of runoff the equivalent of 11 or 12 rain storage barrels with a standard capacity of 55 gallons each.

Of course, the cached water, having coursed down a roof and being untreated, is not of a municipally purified caliber — meaning it's not drinking water. Nonetheless, it's useful.

In rural areas especially and on islands, it's a primary water source; in more urban areas, it's both a means of controlling stormwater and a supply source for small-scale agriculture. Without treatment, the rainwater is a suitable alternative supply for nonpotable purposes, such as laundry, crop and/or landscape irrigation, car washing and toilet flushing. With some filtering, it can become a source of drinking water.

Meanwhile, RWH is getting a lot of new attention from education, business, science and industry. A splendid academic example is the continuing contributions of researchers with the School of Computing, Engineering & Mathematics, Western Sydney University, Penrith, Australia.

The WSU technical investigators have lately conducted and published considerable research, as in a recent special issue of the journal Water. The work is in areas highly relevant to contemporary RWH:

  • urban and suburban agriculture
  • standardization of RWH designs according to region
  • the use of geospatial and spatial technology
  • water supply techniques in arid regions
  • the application of multicriteria analysis and artificial neural networks to RWH

The research repeatedly demonstrates RWH's well-known advantages. In semi-arid regions, it enhances water availability for both living and growing purposes. If widely implemented, RWH systems help local government to delay construction of new dams, pipelines and other parts of the water supply infrastructure. Finally, especially in remote regions, RWH can contribute mightily toward fulfilling sustainable development goals, such as assuring availability and management of the public water supply.

RWH is simply a decentralized, cost-effective and more resilient means of enhancing water security — especially in areas of increasing scarcity — than complex public water supply systems.