New approaches

Instead of using the roof for catchment, the RainSaucer, which looks like an upside down umbrella, collects rain straight from the sky. This decreases the potential for contamination and makes potable water for developing countries a potential application.^[8] Other applications of this free standing rainwater collection approach are sustainable gardening and small plot farming.

A Dutch invention called the Groasis Waterboxx is also useful for growing trees with harvested and stored dew and rainwater.

Traditionally, storm water management using detention basins served a single purpose. However, Optimized Real-Time Control (OptiRTC) lets this infrastructure double as a source of rainwater harvesting without compromising the existing detention capacity.^[10] This has been used in the EPA headquarters to evacuate stored water prior to storm events, thus reducing wet weather flow while ensuring water availability for later reuse. This has the benefit of increasing water quality released and decreasing the volume of water released during combined sewer overflow events.^[11][12]

Generally, check dams are constructed across the streams to enhance the percolation of surface water in to the sub soilstrata. The water percolation in the water impounded area of the check dams, can be enhanced artificially many folds by loosening the sub soil strata / overburden by using ANFO explosives as used in open cast mining. Thus local aquifers can be recharged quickly by using the available surface water fully for using in the dry season.

Benefits Of Rainwater Harvesting

By capturing water directly, we can significantly reduce our reliance on water storage dams. This places less stress on these dams and can potentially reduce the need to expand these dams or build new ones.

Collecting and using your own water can also significantly reduce your water bills.

By capturing water, the flow of stormwater is also reduced and this minimises the likelihood of overloading the stormwater systems in our neighbourhoods.

What About Dirty Roofs?

There are a number of devices (first flush devices) which allow for the first flow of water to the rainwater storage tank to be diverted from the tank. By doing this, any dirt on the roofs of buildings that has built up prior to the rain can be excluded from the tank.

Sizing of Rainwater Storage Tanks

The most appropriately sized rainwater storage can be chosen by quantitatively assessing the performance of various sized storage capacities. By assessing the performance of various sized storage capacities, it is possible to make an informed decision as to what would be the most suitably sized storage capacity for the given application. The input for the assessment is historical daily rainfall data, and the performance of a particular storage capacity can be judged by how much water is required to be supplied from other sources to makeup for any shortfall in demand.

What is rainwater harvesting and why is it Important?

Water is our most precious natural resource and something that most of us take for granted. We are now increasingly becoming aware of the importance of water to our survival and its limited supply, especially in such a dry continent as Australia.

The harvesting of rainwater simply involves the collection of water from surfaces on which rain falls, and subsequently storing this water for later use. Normally water is collected from the roofs of buildings and stored in rainwater tanks. This is very common in rural Australia. Water can also be collected in dams from rain falling on the ground and producing runoff.

Either way, the water collected can be considered to be precious.

• In Bangalore it is mandatory for adoption of RWH for every owner or the occupier of a building having the sital area measuring 60’X40’ and above and for newly constructed building measuring 30’X40’ and above dimension. In this regard BWSSB has initiated and constructed “Rain Water Harvesting Theme Park” in the name of Sir. M. Visvesvaraya in 1.2 acre land situated at 40th cross, 8th main, 5th block Jayanagar Bangalore-41. In this park 26 different type of Rain Water Harvesting models are demonstrated along with the Water conservation tips for inside and outside the main building. The Auditorium on the first floor is set up with Green Air conditioning system and the same will be utilised to arrange the meeting and showing the video clip about the RWH to the Students as well as general public. 
• In the state of Tamil Nadu, rainwater harvesting was made compulsory for every building to avoid groundwater depletion. It gave excellent results within five years, and every state took it as role model. Since its implementation, Chennai saw a 50 percent rise in water level in five years and the water quality significantly improved.
• In Rajasthan, rainwater harvesting has traditionally been practiced by the people of the Thar Desert. There are many ancient water harvesting systems in Rajasthan, which have now been revived.^[23] Water harvesting systems are widely used in other areas of Rajasthan as well, for example the chauka system from the Jaipur district
• At present, in Pune (in Maharashtra), rainwater harvesting is compulsory for any new housing society to be registered.
• An attempt has been made at the Department of Chemical Engineering, IISc, Bangalore to harvest rainwater using upper surface of a solar still, which was used for water distillation^[25]

System setup

Assessing Performance of Different Sized Rainwater Storage Tanks

The performance assessment of various sized storages involves the calculation of the amount of water in storage for a given day. This calculation is based on the water balance shown above. This is a simple calculation, however, using a computer allows this calculation to be completed for many consecutive days of rainfall data. This is equivalent to trial sizing a storage tank size over the period of assessment (over many years).

The computer model completes daily water balance calculations, so that any roof runoff generated from rainfall in that day is calculated. The computer model also calculates the daily level status of the water storage used to hold this rainwater.

During any one day the storage could overflow depending on the amount of roof runoff generated. Likewise, the storage could also be emptied if the volume of water used exceeds the amount of water available from the storage. In this case, water must be supplied from other sources in order to fulfil the water demand. The computer model calculates and sums the amount of water supplied from other sources over the period of assessment. This information can then be used for a comparative assessment of the different amounts of makeup needed with use of different size water storages.

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. 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. The water storage tank size should be large enough to contain the captured water.\

For low-tech systems, there are many low-tech methods used to capture rainwater: rooftop systems, surface water capture, and pumping the rainwater that has already soaked into the ground or captured in reservoirs and storing it into tanks (cisterns).

Before a rainwater harvesting system is built, it's helpful to use digital tools. For instance, if you want to detect if a region has a high rainwater harvesting potential,rainwater harvesting GIS maps can be made using an online to. Or if you need to estimate how much water is needed to fulfill a community's water needs, the Rain is Gain tool helps with this. 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.

Rain Water Harvesting and methods

1. Surface runoff harvesting

In urban area rainwater flows away as surface runoff. This runoff could be caught and used for recharging aquifers by adopting appropriate methods.

2. Roof Top rainwater harvesting

It is a system of catching rainwater where it falls. In rooftop harvesting, the roof becomes the catchments, and the rainwater is collected from the roof of the house/building. It can either be stored in a tank or diverted to artificial recharge system. This method is less expensive and very effective and if implemented properly helps in augmenting the ground water level of the area.

2.1 Components of the roof top rainwater harvesting

The illustrative design of the basic components of roof top rainwater harvesting system is given in the typical schematic diagram

The system mainly constitutes of following sub components:

• Catchments
• Transportation
• First flush
• Filter

Catchments

The surface that receives rainfall directly is the catchment of rainwater harvesting system. It may be terrace, courtyard, or paved or unpaved open ground. The terrace may be flat RCC/stone roof or sloping roof. Therefore the catchment is the area, which actually contributes rainwater to the harvesting system.

Transportation

Rainwater from rooftop should be carried through down take water pipes or drains to storage/harvesting system. Water pipes should be UV resistant (ISI HDPE/PVC pipes) of required capacity. Water from sloping roofs could be caught through gutters and down take pipe. At terraces, mouth of the each drain should have wire mesh to restrict floating material.

First Flush

First flush is a device used to flush off the water received in first shower. The first shower of rains needs to be flushed-off to avoid contaminating storable/rechargeable water by the probable contaminants of the atmosphere and the catchment roof. It will also help in cleaning of silt and other material deposited on roof during dry seasons Provisions of first rain separator should be made at outlet of each drainpipe.

Filter

There is always some skepticism regarding Roof Top Rainwater Harvesting since doubts are raised that rainwater may contaminate groundwater. There is remote possibility of this fear coming true if proper filter mechanism is not adopted. Secondly all care must be taken to see that underground sewer drains are not punctured and no leakage is taking place in close vicinity. Filters are used fro treatment of water to effectively remove turbidity, colour and microorganisms. After first flushing of rainfall, water should pass through filters