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Monday, 30 December 2019

Risk of Contamination in Rooftop Rainwater Harvesting

Enviraj RWH

There has been a growing interest, especially in developing nations like India, in rooftop rainwater harvesting as an alternative source of freshwater. 

Rooftop rainwater harvesting involves the collection and storage of water from rooftops. Generally, rainwater is free from impurities except those picked up by rain from the atmosphere, but the quality of rainwater may deteriorate during harvesting, storage and reuse.

Microbiological Contamination

Microbial contamination of collected rainwater indicated by E. coli (or thermotolerant coliforms) is quite common, particularly in samples collected shortly after rainfall. 

Many research publications from different regions reported 24- 92% of harvested rainwater samples positive for microbial contamination.

Higher microbial concentrations are generally found in the first flush of rainwater, and the level of contamination reduces as the rain continues.

Heavy Metals

Rainwater is slightly acidic in nature and it can dissolve heavy metals and other impurities from materials of the catchment and storage tank.

The elevated levels of zinc and lead have sometimes been reported. This could be from leaching from metallic roofs and storage tanks or atmospheric pollution.

A well-designed rainwater harvesting systems with clean catchments, filtration systems and storage tanks supported by good hygiene can offer portable-water with very low contamination risk, whereas a poorly designed and managed system can pose a high contamination risk.

Stay tuned for our next article, where we will discuss the ways to reduce contamination risks associated with rainwater harvesting.

Thursday, 26 December 2019

Harvest Water from Air

The depletion of freshwater sources and rising water scarcity across the world, companies are now looking to tap the atmosphere that holds around six times as much water as all the world’s rivers.

Estimates of atmospheric water (when liquified) in India is 1,360 BCM which is closed to utilizable water resource of 1,123 BCM (Groundwater - 433 BCM and Surface water -690 BCM). India's current population estimated requirement of 2 BCM safe drinking water annually. 

The solar-powered atmospheric water generator
(Image Source: Sciencemag)
An atmospheric water generator (AWG)s are machines that extract water from humid ambient air. Water vapour in the air is condensed by cooling the air below its dew point, exposing the air to desiccants, or pressurizing the air. 

The contaminants in atmosphere water could be high but it can be removed with the integrated water filtration system.

To date, an industrial AWG of 1,000 litres/day capacity could cost upwards of Rs. 1.0 Lakh, a domestic unit with a 40 litres/day capacity costs between Rs 30k-40K

This apart, the average cost of electricity consumed for 40 L/day Machine works out to be close to Rs 56 a day or Rs 1,680 a month.

Pros and cons of AWG technology:

  • AWG is a very effective technology to harvest water from the atmosphere since all it needs are air and electricity, which can both be obtained from natural energy sources.

  • Even though AWG requires humidity to produce freshwater, it can be placed anywhere.

  • It is valuable to areas that don't support life due to lack of water.
  • AWGs are known to be more expensive than other water harvesting technologies.

  • The efficiency of the system depends on the humidity of the air. They are a less attractive option in places with the dry climate.

  • The contaminants in atmosphere water could be high, particularly for a country like India, which has a dense population. The water filter needs to be properly maintained.

AWG machines have a negligible effect on the environment even if entire India consumes from the source simultaneously. The success of the AWGs will, therefore, depend upon the pricing and efficacy of the product.