Harvesting and using roof-top rainwater - Part 2
Are the filters used for rainwater harvesting easy to maintain? More importantly, how efficient are they in terms of minimising the waste water that flows out?
22 Jun 2013
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This short note is a sequel to my earlier article which analysed the functioning and performance of my Roof-top Rainwater System using Rainy filter. While the earlier article narrated my initial observations on using the Rainy FL-100 filter for direct use of roof water during the monsoon season June-Sept 2012, this article focuses on the maintenance of the filter vis-à-vis its efficiency in terms of minimising the waste water that flows out.

After a few months of the monsoon (by the end of Dec 2012), I realised that the amount of water rejected by the filter gradually increased. 10-15% of water rejection at the time of installing in June 2012, gradually increased and a significant part of rain water was being rejected by the filter by the end of December 2012. I was puzzled at first but later realized the need for removing the filter element inside and cleaning the fine mesh. The onset of the monsoon in June 2013 prompted me make preparations for putting the rainwater harvesting system to best use. I got the roof and my storage tank cleaned and removed the filter mesh element inside the Rainy-100.


Filter element soon after it was taken outFine mesh inside the outer casingThe filter element has an outer casing with holes of a uniform size all over it. The fine mesh that screens the rainwater is located inside this casing. Though there is about half an inch space between the two at the bottom of the element, the casing and the mesh join together at the top of the element. Thus, the cylindrical mesh inside has larger diameter at the top and tapers to the bottom.

As seen from the above pictures, this element was full of dust and clay stuck to the element and inner mesh. I soaked the element in water for about 4 hours and then cleaned it with a brush. This removed the dirt that was exposed on the outer casing. Half of the fine dust that got stuck in the openings on the fine mesh still remained there.

Brushing this dust could be done only on the inner surface of this mesh. As the annular space between the mesh and casing was small and further tapered from bottom to the top, there was no possibility of inserting even a thinner and longer brush (such as a used tooth brush) in the annular space.  Though product descriptions on the company website (www.rainyfilters.com ) claim the filter design to be ‘self-cleaning’ and ‘auto flush out’, it still required some human time and effort to keep this filter in order. 

Filter element after cleaning

More and more pore spaces on the file mesh getting filled up like this results in increased rejection of water from the filter, thus, reducing its efficiency drastically over a few rainy seasons. The company could do away with the outer casing if it were just meant to guard the mesh. That would provide better access to the inner mesh for cleaning and maintenance. 

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