Natural Bank / Bed Filtration: Water Supply Schemes in Uttaranchal, India

Natural purification of water from rivers and lakes through bank and bed filtration has been shown to be quite effective in the state of Uttaranchal (Longitude 77° 34' 27" to 81° 02' 22" E and Latitude 28° 53' 24" to 31° 27' 50" N), India. The subsurface water under the direct influence of surface water is being tapped by (i) tube-wells in Nainital, (ii) infiltration wells in Hardwar, and (iii) uttaranchal wells in adjoining hilly areas of Dehradun. This paper presents quality of surface and subsurface water at three sites. Cost effective water supply schemes have been developed on the basis of lake, bank filtration, river bank filtration and river bed filtration. At Nainital, five tube-wells of different depths (22.6m – 33.35m) are in use to tap the subsurface water from the unconfined aquifer hydraulically connected to lake water. Lake water as such is not potable as it contains unacceptable levels of organic matter in terms of COD (~ 31 mg/L), coliform (~ 17 x 10⁴ MPN/100 mL) and nutrients. On the other hand coliform bacteria, organics and nutrients have not been detected in any of the well water samples over the years. Sixteen infiltration wells located on the bank of the river Ganga and Ganga Canal at Hardwar get water from the unconfined aquifer hydraulically connected to the river and canal. Distance of the infiltration wells from the river/canal varies from 4 to 90m at different locations. Up to 3 log turbidity reduction and 4 log fecal coliform removal (MPN) is achieved through natural bank filtration. The hilly streams normally have permeable strata just below their bed, saturated with water and having continuous sub-surface flow by gravity. Uttaranchal Well is embedded below the stream bed to tap this continuous sub-surface flow which is in direct connectivity with the surface water above it. It is being used successfully for more than 300 rural water supply schemes in different districts of Uttaranchal. Water quality analysis of samples taken from these wells and source water for Dehradun district is carried out in monsoon, the worst season to assess effectiveness of bank/bed filtration. Fecal coliform count and turbidity of water collected from Uttaranchal Wells is 30 times less than that of stream water. River/stream water is highly turbid particularly during rainy season while well waters are quite clear. These improvised-innovation adapted are operative, almost maintenance free, economical, and sustainable.