Rainwater Filters

With the water crisis gripping most parts of India, we are receiving many calls enquiring about rainwater harvesting and Rainwater filtration process/Processes. Most questions are related to how the rainwater can be filtered. 

Many brands of Rainwater filters are available in the market. Mostly they work under two broad principles; 

• Centrifugal Force: The water enters the filter laterally and swirls inside the filter and makes a vortex. The heavier particles fall off due to centrifugal force and relatively clean water pass through the filter. 
• Conventional Gravity Flow (Sand filter): Here the water enters the filter chamber after first rain separation (A method to leave out initial few minutes of rain). The water passes through series of filter media and enters the filter. 

This posts is intended to enlist the main differences between the two types of filter and help people choose the right filter for their needs. 

Below are the main differences between the two types of filters. 

Sl No`	Centrifugal Filter	MSF (Modified sand filter)
1	Quick to install	Elaborate process and time consuming for installation.
2	Looks very elegant	Looks are not great
3	Efficiency  is 70 to 75%	Efficiency is 90-95%
4	Easy to clean	Cleaning is labour intensive
5	Not Self-Cleaning during rains	Not self-cleaning during rains
6	Wall mounted	Ground Mounted.
7	Design is just few years old	Conventional time tested design.
8	Works on centrifugal force	Works only on gravity.
9	Only mesh for filtration	Mesh ,graded metal, cinder and activated carbon for Filtration.
10	Cannot support rainfall greater than 80 mm/hour.	Can support any rainfall.
11	Filtration is very basic	Filtration is elaborate.
12.	No sedimentation tank possible	Sedimentation tank is a part of the design.
13.	Loss during rains is very substantial	No loss during rain.
14	Minor clogs can result in all the water getting wasted.	No loss due to any clogs. However, it is important to clean the filer regularly.
15	No backwash	Backwash is possible after every rain.
16	Automatic flush out if filter is clogged	No automatic flush out.
17	Expensive but branded	Unbranded.
18	Standard design	Custom built.
19	Civil works is less	Civil works is more.
20	Running cost is almost negligible if the mesh does not break due to sand or abrasive material getting inside the filter.	Running cost is little higher