Rain Water Harvesting

Environment Studies

RAIN? How is rain made?

Rain is liquid water in the form of droplets that have condensed from atmospheric water vapor and then precipitated—that is, become heavy enough to fall under gravity

When the sun shines, it heats the water in the rivers and seas.

The water changes into water vapour. This water vapour rises up into the sky.

The water vapour cools into droplets and becomes a cloud.

When there are too many droplets in the cloud, they fall towards the ground as rain.

WATER CYCLEEvaporation:

Heat from the Sun causes water on Earth (in oceans, lakes etc) to evaporate (turn from liquid into gas) and rise into the sky. This water vapor collects in the sky in the form of clouds.

Condensation:

As water vapor in the clouds cools down it becomes water again, this process is called condensation.

Precipitation:

Water falls from the sky in the form of rain, snow, hail, or sleet, this process is called precipitation.

Collection:

Oceans and lakes collect water that has fallen. Water evaporates into the sky again and the cycle continues.

Transpiration:

In a process similar to sweating, plants lose water which is absorbed into the atmosphere much like evaporation. The combination of evaporation and transpiration is known as evapotranspiration.

Sublimation:

It is possible for a solid to transform into a gas directly (without becoming a liquid). The most common example of sublimation is dry ice (solid carbon dioxide) which sublimes at normal air temperature. Under certain conditions snow and ice can also sublime. 

Rain Water

HarvestingIt is the process of collecting and storing water for future productive use.

Commonly used systems are constructed of three principal components; namely, the catchment area, the collection device, and the conveyance system.

Components• Catchment surface - rooftop or other raised solid surface. The best catchment systems have hard,

smooth surfaces such as metal roofs or concrete areas. The amount of water harvested depends on the quantity of rainfall, and the size of the surface and the slope of the catchment area.

• Gutters and downspouts - also known as distribution systems that channel the water from the catchment area to a holding container such as a barrel, cistern, planted area, etc.

• Leaf screens - a screen that removes or catches debris.

• Roof washers - a device that diverts the "first flush" of rain before it enters the storage tank. Most rainwater suppliers recommend that the "first flush" of water is diverted to an outside area of the storage system, since the catchment surface may accumulate bird droppings, debris and other pollution.

Storage tanks - In general, the storage tank is the most expensive component of a rainwater harvesting system. There are numerous types and styles of storage tanks available. Storage can be above-ground or underground. Storage containers can be made from galvanized steel, wood, concrete, clay, plastic, fiberglass, polyethylene, masonry, etc. Examples of above-ground storage include; cisterns, barrels, tanks, garbage cans, above ground swimming pools, etc. Storage tank prices vary based on different variables such as size, material and complexity. To inhibit the growth of algae, storage tanks should be opaque and preferably placed away from direct sunlight. The tanks should also be placed close to the areas of use and supply line to reduce the distance over which the water is delivered. Also consider placing the storage at an elevated area to take advantage of gravity flow. The tank should always be placed on a stable and level area to prevent it from leaning and possibly collapsing.

• Delivery systems - gravity-fed or pumped to the landscape or other end use areas.

• Purification/treatment system - needed for potable systems to make the water safe for human consumption, filtration systems and certification requirements.

• Makes use of a natural resource and reduces flooding, storm water runoff, erosion, and contamination of surface water with pesticides, sediment, metals, and fertilizers

• Reduces the need for imported water

• Excellent source of water for landscape irrigation, with no chemicals such as fluoride and chlorine, and no dissolved salts and minerals from the soil

• Home systems can be relatively simple to install and operate May reduce your water bill

• Promotes both water and energy conservation

• No filtration system required for landscape irrigation

Advantages

DisadvantagesLimited and uncertain local rainfall

•Can be costly to install - rainwater storage and delivery systems can cost between $200 to $2,000+ depending on the size and sophistication of the system

•The payback period varies depending on the size of storage and complexity of the system

•Can take considerable amount of time to "pay for itself"

•Requires some technical skills to install and provide regular maintenance

•If not installed correctly, may attract mosquitoes (i.e.; West Nile Disease and other waterborne illnesses)

•Certain roof types may seep chemicals, pesticides, and other pollutants into the water that can harm the plants

•Rainwater collected during the first rain season is generally not needed by plants until the dry season. Once catchment is full, cannot take advantage of future rains

Drink ITThough rainwater as it falls from the clouds is very pure, it does pick up dirt, dust and bacteria once it falls on the roof. It is very necessary to therefore check the quality of the water before using it for consumption.

Form of deactivating bacteria and making water fit for consumption is called SODIS – Solar disinfection of water.

From the tap in the rainwater storage tank fill the bottle to the mark provided. Close the cap tightly. Bring the bottle back to a safe place in a room. Observe for 24 to 48 hours. If the water turns black in the bottle then it is micro-biologically contaminated and requires treatment before being used for drinking. If the water color stays brown, then the water is fit for drinking.

WATER FACTSDishwashers are more water efficient and effective than hand washing.

Washing machines use approximately 14% of domestic water

A typical family uses 70,000 liters year on clothes washing, and outside use

Approximately 600 gallons of rainwater can be harvested from one inch of rain falling on a 1,000 square foot roof.

A leaky tap in the office toilets or canteen kitchen can waste 60 litres an hour (5mm stream) or nearly half your daily usage.

Rain is recycled water that evaporated from our world's lakes, rivers, oceans, seas etc

Rain occurs on other planets in our Solar System but it is different to the rain we experience here on Earth. For example, rain on Venus is made of sulfuric acid and due to the intense heat it evaporates before it even reaches the surface!

THANK YOU!