Rainwater harvesting strategies

By: Admin
Jul 31 2017

Water scarcity is set to be a more menacing problem in India without the immediate implementation of proper corrective measures. India largely depends on its groundwater resources for water supply, and there is intense pressure on this sole resource. The pressure of urbanity in highly populated cities is already evident in water scarcity in many places. High-rises and slums alike need water to survive, and so the pressure is severe.

Water is an important natural resource and is the very basis of our life. We use water for drinking, irrigation, industry, transport and for the production of hydro-electricity. Water is a cyclic resource which can be used again and again after cleaning. The best way to conserve water is its judicious use.

Added to this is the water requirement of industries crowding the urban scenario. Plus, in the surrounding villages near the cities draw out groundwater for agriculture and livelihood. All these activities put immense pressure on groundwater, which is dwindling away at a rate faster than it is getting refilled. All these factors points out to the mandatory need for implementation of water harvesting techniques.

This includes two broad parameters, groundwater and rainwater management. The monsoon rains provide the supply of groundwater. In seasons, when monsoon is scarce, groundwater levels plummet substantially. In extreme situations, draught situations may develop. Cities cannot get much of the monsoon rain to store as groundwater. The concrete of the cityscape does not absorb water, and a lot of the rainwater just wastes. The wastewater problem is also a huge issue. Public consciousness on water consciousness is yet to develop and a huge number of roadside taps do not have any faucets at all. Water comes out and wastes indiscriminately.

There are several aspects of groundwater management. The key focus is to recycle water and make it easily available for everyone. Identification of aquifers using advanced hydro-geological instruments is important for proper mapping and usage of groundwater. This water is also important for agricultural purposes. So, a proper plan must be in place defining agricultural use and personal use of the water resource. The combination of rainwater and groundwater can see to that India does not suffer from the impending doom of huge water scarcity.

India is one of the largest users of groundwater resources. The country largely depends on this water source for daily usages, industries, and agriculture. In fact, India's groundwater utility is way more than China and the USA.


In a monsoon rich country like India, rainwater harvesting must receive its due importance. In cities, most of the rainwater is lost as waste water. In villages, where there are open fields, still the rainwater seeps within the ground to nourish the aquifers. The harvesting of rainwater must begin at the homes. Homeowners can manage the water supply during the monsoon through harvesting the rainwater. This involves collection, storage, treatment and recycling of the water. You need to find a service that can provide all these solutions. Look for a service with diverse industry experience and having a commitment to the society. Find the people using the most advanced methods of sustainable water conservation. The service must be able educate people on need of long-term water conservation methods like planting trees.

The rapid urbanization and the constant expansion of urban areas during the last decades have locally led to increasing water shortage. Rainwater harvesting (RWH) systems have the potential to be an important contributor to urban water self-sufficiency.

According to the environmental assessment, the tank location and distribution strategy chosen were the most important variables in the optimization of RWH systems. Roof tank strategies present fewer impacts than their underground tank equivalents because they enhance energy and material savings, and their reinforcement requirements can be accounted for within the safety factors of the building structure without the tank. Among roof tanks and depending on the height, a distribution strategy that concentrates demand in a laundry room was the preferable option, resulting in reductions from 25 to 54 % in most of the selected impact categories compared to distribution throughout the building.

Rainwater harvesting means capturing and storing rain that falls on-site (usually on roofs). It is generally used for irrigation and toilet flushing or other grey water uses, though it can also be used for drinking water if it is adequately treated. Capturing rainwater can be a valuable way to reduce or even eliminate a building's use of municipal potable water, without requiring reductions in water use by occupants. However, it is of course more effective in rainy climates than dry ones.

Rainwater harvesting systems are measured by their area for collecting water (in m2 or ft2) and the volume of water they store (in liters or gallons). Simple rainwater collection systems have three main elements: the roof or other catchment area, the storage tank(s), and the gutter and other piping that directs the water from the catchment area to the tank.

Advanced systems may also use a pump to pull water from the tank to where it is used, and may purify the water with additional devices such as filters and ultraviolet disinfection.
If the rainwater is meant for drinking or watering gardens, be sure to choose a tank material that does not leach toxins or foster pathogens. For example, galvanized steel tanks are lined with polyethylene or other food-grade liner.
If the rainwater is collected from a roof is meant for drinking or watering gardens, be sure to choose roofing materials that do not leach toxins. For instance, asphalt shingles leach toxins into water, while metal roofs or slate shingles do not.
 To size a system for a site, you must choose the water collecting area to supply enough volume of water for the site occupants, given the site's rainfall patterns.  The simplest equation for system sizing is this:
(Volume) = (Area) • (Precipitation) • (% Efficiency)
Volume is the amount of rain harvested in that time period, measured in liters. Area is the rainwater capture area, measured in m2. Precipitation is the amount of rainfall in that time period (in mm). Efficiency is the percent of water actually captured, as opposed to splashing out of the system somewhere; it is usually 75% - 90%.
The volume of water needed by the occupants will vary based on the number of occupants, the amount of time they spend on site, the activities they engage in, and the equipment or processes used on site.

Weather data from meteorological department files can be used to determine rainfall patterns. These will be in mm or inches of rain.
Be sure to calculate average monthly rainfall for the different months of the year, not simply an annual total. Most sites have much more rainfall in some seasons than others, and excess water can always be drained, but a lack of water requires municipal water use to compensate.
Different gutter systems, different roof pitches, and different materials can affect system efficiency. For example, lower-pitch roofs cause less loss than steeply-pitched roofs.

There is no one standard recommended size for rainwater storage tanks. The size depends on the site's water needs, the weather, and whether the site is connected to a municipal water supply or not. While bigger tanks allow for more water independence, the tank is usually the most expensive part of the system.
Rainwater harvesting systems can range in complexity, from systems that can be installed with minimal skills, to automated systems that require advanced setup and installation. The basic rainwater harvesting system is more of a plumbing job than a technical job, as all the outlets from the building terrace are connected through a pipe to an underground tank that stores water.

Systems are ideally sized to meet the water demand throughout the dry season, since it must be big enough to support daily water consumption. Specifically, the rainfall capturing area such as a building roof must be large enough to maintain adequate flow of water. The water storage tank size should be large enough to contain the captured water.
For low-tech systems, many low-tech methods are used to capture rainwater: rooftop systemssurface water capture, and pumping the rainwater that has already soaked into the ground or captured in reservoirs and storing it in tanks (cisterns).
Before a rainwater harvesting system is built, use of digital tools is useful. For instance, to detect if a region has a high rainwater harvesting potential, rainwater-harvesting GIS maps can be made using an online interactive tool.
Or, to estimate how much water is needed to fulfill a community's water needs, the Rain is Gain tool helps. Tools like these can save time and money before a commitment to build a system is undertaken, in addition to making the project sustainable and last a long time.
Contemporary system designs require an analysis of not only the economic and technical performance of a system, but also the environmental performance. 
Lifecycle assessment is a methodology used to evaluate the environmental impacts of a precut or systems, from cradle-to-grave of its lifetime.
To address the functional parameters of rainwater harvesting systems, a new metric was developed - the demand to supply ratio (D/S) - identifying the ideal building design (supply) and function (demand) in regard to the environmental performance of rainwater harvesting for toilet flushing. With the idea that supply of rainwater not only saves the potable water, but also saves the stormwater entering the combined sewer network (thereby requiring treatment), the savings in environmental emissions were higher if the buildings are connected to a combined sewer network compared to separate one.


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