Groundwater dip: quantum, quality
the latest groundwater report of Karnataka, brought out by the Department of Mines and Geology (dmg) , shows that entire Bangalore is an overexploited zone. The 2004 study puts 55 taluka s in the overexploited category. The situation is worst in Kolar and Tumkur, apart from Bangalore's rural and urban areas. Besides the quantum of the resource, the quality of groundwater in Bangalore city is also alarming due to contamination with sewage and industrial effluents. Groundwater meets 40 per cent of the city's domestic potable water needs.
An analysis of 918 water samples collected from 735 locations shows that at 370 locations, the groundwater is not suitable for domestic use as per the specifications of the groundwater quality report of Bangalore city, 2003. Iron content in the groundwater was over 1 milligramme per litre (mg/l) in many places; the permissible limit is 0.3 mg/l. Of the 918 samples, 116 had iron content over 1 mg/l; at a few locations, it was over 6 mg/l."High iron content is due to rusting pipes and industrial contamination," says Shashi Rekha, chief chemist, dmg. Regarding nitrate concentration of over 50 mg/l in 262 samples, she says it indicates heavy sewage contamination and domestic pollution.Also, hardness exceeds the permissible limit of 600 mg/l in 51 samples -- a result of sewage contamination. The pH value is below the permissible range of 6.5 to 8.5 in 106 samples, another result of industrial pollution.
To determine bacteriological pollution, 100 samples were collected from areas without underground drainage systems to test for total coliforms and fecal coliforms. Bacteriological pollution of upto 23 most probable number per 100 millilitres (mpn/100 ml) was found in 74 samples; the permissible limit for drinking water (without chlorination) is 0 mpn /100 ml. The report urges checking sewage and industrial waste pollution and stresses on the need for rainwater harvesting.