Fresh Water Conservation
Billions of people will lack access to safe water, sanitation and hygiene in 2030 unless progress quadruples – WHO, UNICEF
Latest estimates reveal that 3 in 10 people worldwide could not wash their hands with soap and water at home during the COVID-19 pandemic
Water covers 71% of our planet, and it is easy to think that it will always be plentiful. However, freshwater—the stuff we drink, bathe in, irrigate our farm fields with—is incredibly rare. Only 2% of the world’s water is fresh water, and two-thirds of that is tucked away in frozen glaciers or otherwise unavailable for our use. As a result, some 1.1 billion people worldwide lack access to water, and a total of 2.7 billion find water scarce for at least one month of the year.
Inadequate sanitation is also a problem for 2.4 billion people—they are exposed to diseases, such as cholera and typhoid fever, and other water-borne illnesses. Two million people, mostly children, die each year from diarrheal diseases alone. Many of the water systems that keep ecosystems thriving and feed a growing human population have become stressed. Rivers, lakes and aquifers are drying up or becoming too polluted to use. More than half the world’s wetlands have disappeared. Agriculture consumes more water than any other source and wastes much of that through inefficiencies. Climate change is altering patterns of weather and water around the world, causing shortages and droughts in some areas and floods in others.
At the current consumption rate, this situation will only get worse. By 2025, two-thirds of the world’s population may face water shortages. And ecosystems around the world will suffer even more.
The human population has successfully harnessed many of the world’s natural waterways—building dams, water wells, vast irrigation systems and other structures that have allowed civilizations to grow and thrive. But water systems are increasingly stressed, and some rivers, lakes and aquifers are drying up. Water pollution comes from many sources including pesticides and fertilizers that wash away from farms, untreated human wastewater, and industrial waste. Even groundwater is not safe from pollution, as many pollutants can leach into underground aquifers. Some effects are immediate, as when harmful bacteria from human waste contaminate water and make it unfit to drink or swim in. In other instances—such as toxic substances from industrial processes—it may take years to build up in the environment and food chain before their effects are fully recognized.
Agriculture uses 70% of the world’s accessible freshwater, but some 60% of this is wasted due to leaky irrigation systems, inefficient application methods as well as the cultivation of crops that are too thirsty for the environment in which they are grown. This wasteful use of water is drying out rivers, lakes and underground aquifers. Many countries that produce large amounts of food—including India, China, Australia, Spain and the United States—have reached or are close to reaching their water resource limits. Added to these thirsty crops are the fact that agriculture also generates considerable freshwater pollution – both through fertilizers as well as pesticides – all of which affect both humans and other species.
Impact
About half of the world’s wetlands have been destroyed since 1900. Some of the most productive habitats on the planet, wetlands support high concentrations of animals—including mammals, birds, fish and invertebrates—and serve as nurseries for many of these species. Wetlands also support the cultivation of rice, a staple in the diet of half the world’s population. And they provide a range of ecosystem services that benefit humanity, including water filtration, storm protection, flood control and recreation.
When water becomes scarce, natural landscapes often lose out. The Aral Sea in central Asia was once the world’s fourth largest freshwater lake. But in only three decades, the sea has lost an area the size of Lake Michigan. It is now as salty as an ocean due to the excessive pollution and the diversion of water for irrigation and power generation. As the sea has retracted, it has left polluted land. This ecological catastrophe has created food shortages and resulted in a rise in infant mortality and a decrease in life expectancy for the nearby population.
PART I: Saving Freshwater: What is Rainwater harvesting?
Rainwater harvesting is the simple process or technology used to conserve Rainwater by collecting, storing, conveying and purifying of Rainwater that runs off from rooftops, parks, roads, open grounds, etc. for later use.
How to Harvest the Rainwater?
Rainwater harvesting systems consists of the following components:
- Catchment- Used to collect and store the captured Rainwater.
- Conveyance system – It is used to transport the harvested water from the catchment to the recharge zone.
- Flush- It is used to flush out the first spell of rain.
- Filter – Used for filtering the collected Rainwater and remove pollutants.
- Tanks and the recharge structures: Used to store the filtered water which is ready to use.
The process of rainwater harvesting involves the collection and the storage of rainwater with the help of artificially designed systems that run off naturally or man-made catchment areas like- the rooftop, compounds, rock surface, hill slopes, artificially repaired impervious or semi-pervious land surface. Several factors play a vital role in the amount of water harvested. Some of these factors are:
- The quantum of runoff
- Features of the catchments
- Impact on the environment
- Availability of the technology
- The capacity of the storage tanks
- Types of the roof, its slope and its materials
- The frequency, quantity and the quality of the rainfall
- The speed and ease with which the Rainwater penetrates through the subsoil to recharge the groundwater.
What are the different methods of rainwater harvesting?
The different methods of rainwater harvesting include:
- Rooftop rainwater harvesting.
- Surface runoff harvesting.
- First, flush.
- Transportation.
- Catchment.
- Filter.
Why do we Harvest Rainwater?
The rainwater harvesting system is one of the best methods practiced and followed to support the conservation of water. Today, scarcity of good quality water has become a significant cause of concern. However, Rainwater, which is pure and of good quality, can be used for irrigation, washing, cleaning, bathing, cooking and also for other livestock requirements. The benefits of rainwater harvesting system are listed below:
- Less cost.
- Helps in reducing the water bill.
- Decreases the demand for water.
- Reduces the need for imported water.
- Promotes both water and energy conservation.
- Improves the quality and quantity of groundwater.
- Does not require a filtration system for landscape irrigation.
- This technology is relatively simple, easy to install and operate.
- It reduces soil erosion, stormwater runoff, flooding, and pollution of surface water with fertilizers, pesticides, metals and other sediments.
- It is an excellent source of water for landscape irrigation with no chemicals and dissolved salts and free from all minerals.
PART II: Saving Freshwater: What is Rainwater harvesting?
Why Recharge?
With an ever increasing demand for water, it’s only natural that water conservation measures would grow in importance. One such measure is ground water recharge, which replenishes aquifers. But instead of waiting for time and Mother Nature to absorb and filter surface water, artificial ground water recharge can be performed. This is done by channeling surplus surface water deeper into the ground. Artificial recharge serves a combination of benefits, such as:
- replenishing the underground aquifer
- acting as storage for surplus rainwater, which can then be recovered during times of water scarcity
- preventing intrusion of sea water into the aquifer in coastal areas
- maintaining base flows in streams
- raising the ground water level, which reduces the costs of pumping
Artificial recharge is common in areas with limited surface water availability, since there is a strong need for ground water for drinking and agriculture.
Recharge Processes
Surface Infiltration
Artificial recharge can be accomplished through surface infiltration or a deep injection well. Surface infiltration systems begin by creating shallow basins on the land’s surface. Water is dumped into these basins for infiltration. These systems depend on the availability of permeable soils capable of high infiltration rates (around 10 feet per day). This is because when water passes through soil layers, many physical, chemical and biological pollutants are filtered out.
One downside to surface infiltration systems is water loss from evaporation (from the wet top soil). But this loss is still considerably less than the amount of water that can potentially infiltrate into the ground.
In a surface infiltration basin, some of the factors that influence infiltration rates are:
- the depth of the infiltration basin
- the number of suspended particles in the water used for infiltration
- the ground water level
Shallow infiltration basins tend to result in better infiltration rates compared to deeper basins. Also, higher ground water levels in the area where infiltration is performed will hamper infiltration rates.
In general, the vertical distance between the infiltration basin’s water surface and the ground water level should be at least twice the infiltration basin’s width. Another design consideration pertains to water quality. High ground water levels mean fewer soil layers are available for filtration. When the quality of the water entering the ground is questionable, it’s safer not to have the infiltration system where ground water levels are high.
Deep Injection Well
The other mode of infiltration is through injection wells. These are appropriate when the soil surface is not permeable, or if large tracts of land aren’t available for setting up a surface infiltration system. An injection well system consists of a:
- casing
- pipe inside the casing to inject the water into the aquifer
- gravel pack
- well screen where the pipe merges with the aquifer
The injection well system is prone to clogging at the interface between the gravel pack and the aquifer. This can adversely impact infiltration rates. This can be resolved by pumping the water out periodically (this can range from 20 minutes every day to a few times a year). How often pumping is necessary depends on the reduction in infiltration rates – higher reduction rates necessitate frequent pumping. A prerequisite to prevent clogging is by pretreating the water to remove suspended solids and other nutrients such as phosphorous and nitrogen.
Artificial Recharge Through Wells in India
In India, artificial recharge is accomplished through recharge wells. In comparison to an injection well, recharge wells are much wider in diameter (they range from 3 feet to 10 feet) and are more shallow in depth (20 feet to 40 feet). Recharge wells are in the storm water drains, since these drains receive the maximum flow volume of surface rain water runoff.
Recharge wells are made by digging a pit in the designated location and then lowering pre-cast concrete rings into the pit. The rings are stacked one on top of the other. The top is covered with a reinforced cement concrete slab with an access cover. A very simple drain filter and silt trap is incorporated into the drain just before the recharge well. They serve to block floating debris and trap heavy soil. Beyond this, no additional filtration is required since the water will pass through layers of soil from the bottom of the well, and soil is the best natural filtration agent.
Recharge wells are generally seen as a mechanism to replenish the shallow aquifers, and over time, the deeper hard rock aquifer as well. In some cases, over a period of sustained recharge, the recharge wells can become discharge wells due to the increase in the ground water table.
