Rainwater Harvesting Methodologies:
Roof Rain Water Harvesting:
The roof top area is used as the catchment area for the rainfall in urban areas. The collection and storage sizes and systems need to be optimized for the Rainwater Harvesting systems in such cases.
Watershed based Rain Water Harvesting:
A watershed consists of a land and water region bounded by ridge lines or other such drainage divides within which the water flowing as surface runoff gets collected and flows out of the watershed along a network of channels or through a single outlet into a lager river or lake. Rainwater harvesting, for a common single watershed, is generally taken up in most of the rural areas. As the cost of land is less and it is available in plenty, surface spreading techniques are generally effectively adopted in such regions.
The cost of municipally supplied water nationwide has increased by 9.8% from 1998 to 2001, 4% between 2001 and 2002, and 27% in the last five years. Prices will continue to rise because of increasing costs to treat water to adapt to EPA’s Safe Drinking Water Act guidelines, upgrade declining infrastructures and instill conservation programs. Most US infrastructure was installed soon after World War II and is now past the 50 year expected lifespan. Therefore, water costs are sure to rise to help offset the replacement/rehabilitation cost. Reducing potable water demand through rainwater harvesting could eliminate the need for infrastructure expansion.
Rainwater harvesting’s economic feasibility can also be calculated by its synergistic values. Rainwater is soft, which means less detergent is used and released into the environment. Also, rainwater harvesting systems with a connected vaporization system can raise site humidity and create a healthier microclimate. This is ideal for city areas dealing with air pollution. Likewise, utilizing rainwater as opposed to municipal and well water, benefits local streams, lakes, ponds and groundwater sources since less water will be pulled from these sources. Such benefits may not have a direct price tag but their value is long lasting and considerable.
In some urban areas, rooftop runoff is directed to storm drains and then to water treatment facilities. These large pipes are expensive to install and travel many miles through urban areas. When a heavy rainfall occurs, the water treatment facilities are overwhelmed with stormwater causing systems to overflow and even contaminate local waterways with untreated sewage. Classifying rainwater as sewage is unnecessary, wastes resources and causes pollution. Through a downspout disconnect program, many cities have reduced the number of downspouts connected to sewer systems. In doing so, rooftop runoff is instead land applied. While the disconnect program addresses wastewater treatment overloading, it does not necessarily address nonpoint source pollution from stormwater runoff. In fact, inappropriately directed downspouts (i.e. to impervious surfaces) can increase non-point source pollution.
The economic feasibility of harvesting rainwater is based on many factors, i.e. precipitation frequency, water consumption needs, prices of local water and wastewater treatment and the cost of installation and maintenance. More importantly is the long-term economic feasibility, which is based on the building’s operational lifespan and system design. The combination of a high building lifespan of at least 40 years, high quality and sustainable prefabricated components and minimum system servicing needs equates to rainwater harvesting being economically feasible and ecologically sensitive.