There are good opportunities for Rainwater harvesting in Kerala because Kerala

Kerala

or Keralam is an Indian state located on the Malabar coast of south-west India. It was created on 1 November 1956 by the States Reorganisation Act by combining various Malayalam speaking regions....

 is blessed with two rainy seasons

Wet season

The the wet season, or rainy season, is the time of year, covering one or more months, when most of the average annual rainfall in a region occurs. The term green season is also sometimes used as a euphemism by tourist authorities. Areas with wet seasons are dispersed across portions of the...

. Kerala faces severe water scarcity between February and mid May every year. During summer, there are
drinking water shortages. During this period drinking water

Drinking water

Drinking water or potable water is water pure enough to be consumed or used with low risk of immediate or long term harm. In most developed countries, the water supplied to households, commerce and industry is all of drinking water standard, even though only a very small proportion is actually...

 and other water purposes become unavailable. This is expected in the coming years. In spite of 44 rivers and world's largest water well

Water well

A water well is an excavation or structure created in the ground by digging, driving, boring or drilling to access groundwater in underground aquifers. The well water is drawn by an electric submersible pump, a trash pump, a vertical turbine pump, a handpump or a mechanical pump...

 density, per capita surface water

Surface water

Surface water is water collecting on the ground or in a stream, river, lake, wetland, or ocean; it is related to water collecting as groundwater or atmospheric water....

 and groundwater

Groundwater

Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock...

 availability of the State is lower than that of arid

Arid

A region is said to be arid when it is characterized by a severe lack of available water, to the extent of hindering or even preventing the growth and development of plant and animal life...

 States of India. Moreover, Kerala has one of the lowest per capita rainwater availability in the Indian sub-continent and it is still decreasing over the time, even though it receives 3000 mm of rainfall, which is around 3 times the Indian national average. The high variations in spatial and temporal rainfall add to the complexity of problems associated with water management faced by the State.

Overview

Rainwater harvesting

Rainwater harvesting

Rainwater harvesting is the accumulating and storing of rainwater for reuse before it reaches the aquifer. It has been used to provide drinking water, water for livestock, water for irrigation, as well as other typical uses. Rainwater collected from the roofs of houses and local institutions can...

, irrespective of the technology used, essentially means harvesting and storing water in days of abundance, for use in lean days. Storing of rainwater can be done in two ways; (i) storing in an artificial storage and (ii) in the soil media as groundwater. The former is more specifically called roof water harvesting and is rather a temporary measure, focusing on human needs providing immediate relief from drinking water scarcity, while the latter has the potential to provide sustainable relief from water scarcity, addressing the needs of all living classes in nature. Through the proposed individual rainwater harvesting, units will be made available to the beneficiaries. Rain water harvesting has gained popularity in Kerala through various projects implemented by different agencies. the Rain Water Harvesting Campaign of the Government and publicity by various media are responsible for popularizing rain water harvesting in the state. Rainwater harvesting is viewed as a water security measure for the State of Kerala, with two broad types of programmes.

Down pipe and first flush arrangement

This is an arrangement to prevent the dust and other unwanted materials that may be seen on the roof, from reaching the storage tank. By fitting a down pipe with an end cap or valve can ensure that the washed water from the roof does not reach the storage tank. It is always safe to ensure that the first flush arrangement remains open during non-
rainy days and should be closed after first rain up to the satisfaction of the end user.

Filter unit

The rainwater collected from the roof should be allowed to reach the storage tank only through a filtering mechanism. Rubble

Rubble

Rubble is broken stone, of irregular size, shape and texture. This word is closely connected in derivation with "rubbish", which was formerly also applied to what we now call "rubble". Rubble naturally found in the soil is known also as brash...

, sand

Sand

Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...

 and charcoal

Charcoal

Charcoal is the dark grey residue consisting of carbon, and any remaining ash, obtained by removing water and other volatile constituents from animal and vegetation substances. Charcoal is usually produced by slow pyrolysis, the heating of wood or other substances in the absence of oxygen...

, as used in the traditional three-pot filtration

Filtration

Filtration is commonly the mechanical or physical operation which is used for the separation of solids from fluids by interposing a medium through which only the fluid can pass...

, can be adopted here. 10 cm thick 20mm rubbles, 10 cm thick charcoal/coconut

Coconut

The coconut palm, Cocos nucifera, is a member of the family Arecaceae . It is the only accepted species in the genus Cocos. The term coconut can refer to the entire coconut palm, the seed, or the fruit, which is not a botanical nut. The spelling cocoanut is an old-fashioned form of the word...

 shell, 15 cm thick coarse sand, 5 cm thick 6mm rubbles etc. may be arranged from bottom to top in the filter unit. The water that is passed through this filter should remain safe for a long period of storage. Charcoal/coconut shell is added to eliminate gaseous pollutants.

Storage tank

Mainly three types of storage tanks are constructed for roof water harvesting. They are aboveground, underground or sub surface tanks.

Provision for drawing water and spill over

For drawing water from the storage tanks any method may be adopted provided it shall be drawn only when needed. The easier the method adopted for drawing water, the more will be the chances for its misuse. Three types of drawing water are usually adopted. They are by using a tap

Tap (valve)

A tap is a valve controlling release of liquids or gas. In the British Isles and most of the Commonwealth, the word is used for any everyday type of valve, particularly the fittings that control water supply to bathtubs and sinks. In the U.S., the term "tap" is more often used for beer taps,...

 (small capacity tanks with basement and over ground tanks), hand pump

Hand pump

Hand pumps are manually operated pumps; they use human power and mechanical advantage to move fluids or air from one place to another. They are widely used in every country in the world for a variety of industrial, marine, irrigation and leisure activities...

 (under ground tanks) or electric pump sets (large capacity tanks).

Maintenance

• Before collecting water the roof, gutters and tank should be cleaned
• Let the first 2-3 rains flow out through the first flush system
• Remember to clean the tank once in a year
• Replace the filtering agents every year
• Keep the tank and surroundings clean and hygenic
• Apply white cement on the tank every year
• Make sure that sunlight does not pass through the manhole
• Remember to preserve water and use it judiciously