Effect of Rainwater Harvesting on the Amounts of Some Heavy Metals, in the Ground Water of

In the present study water samples, from various societies of East Zone of Dwarka subcity of New Delhi have been collected where rainwater-harvesting systems are installed. The impact of rainwater harvesting on the amounts of heavy metals in ground water has been studied by collecting water samples from these selected sites in the months before and after the rain. In study the difference between the values of some of the heavy metals in ground water, collected before and after rain, has been found. The present study reveals that the rainwater harvesting suitably reduced the amounts of heavy metals in under ground water and has improved the quality of ground water.


INTRODUCTION
Heavy metals are integral components of drinking water and have an important role in ascertaining the quality of drinking water for the drinking purpose.The amounts of the heavy metals should be adequately and as per the guidelines values provided by World Health Organization.Chromium appears to be necessary for glucose and lipid metabolism and for utilization of amino acids in several systems.It also appears to be important in the prevention of mild diabetes and atherosclerosis in humans 8 .Because of low solubility of chromium generally, the level found in water is usually low (9.7µg/L) 9 .Drinking water normally contains very low concentration of cadmium of the order of 1 µg/L or less 10,[11][12][13] ; occasionally, levels up to 5 µg/L have been reported 10 and on rare occasion levels up to 10 µg/L have been detected 14 .
The present study is related to the improvement in ground water quality using rainwater harvesting, wherein the physicochemical parameters have been determined to ascertain whether rainwater harvesting is useful for the ground water.The physicochemical parameters found improving the quality of ground water.Additionally, the studies on heavy metals were also conducted.During the study various samples, collected from the predetermined sites, were analyzed and amounts of heavy metals were determined.Subsequently, it was studied on the basis of determined values that how the rainwater harvesting is useful for the ground water quality.

Reagents and Instruments
Atomic Absorption Spectrophotometer (AAS-300, FIAS) was used for determining the amounts of heavy metals in the below-mentioned water samples.Atomic Absorption Spectroscopy is one of the most widely used methods in analytical chemistry.This phenomenon can be divided into two major processes (i) The production of free atoms from the sample and (ii) the absorption of radiation from an external source by these atoms.
The conversion of analyst in solution to free atoms in the flame is done by the flam atomizer.
Here the metallic elements from its dissolved salts in the sample solution are converted into free atoms of the elements, by converting the sample solution into its aerosol.This aerosol when enters the flame, solvent is evaporated leaving small particles of the dry solid which is then converted into its vapor.Finally, this dissociates to give neutral free atoms.Some of these atoms are thermally excited by the flame but most remain in the ground state.These ground state atoms can absorb radiation of a particular wavelength that is produced by a special source made from that element.The wavelength of radiation given off by the source are the same as those absorbed by the atoms in the flame.The absorption follows Beers' Law i.e. the absorbance is directly proportional to the path length in the flame and to the concentration of atomic vapour in the flame.However the path length may be held constant and the concentration of atomic vapour is directly proportional to the concentration of the analyte in the solution, which is displayed on electronic read out.

Collection of water samples
Each fifteen ground water samples were collected on 1 st day of July 2004 when it was almost no rain.The samples from the same sites were then again collected on 1 st day of January 2005 after the rainy season.All samples were tightly sealed and immediately taken to the laboratory for analysis.During the analysis all samples were stored in dark and cool environment (at 4°C approx.)

Sampling sites
Ground water samples collected from fifteen societies where rainwater-harvesting systems are installed.The names of the societies are as follows.

Sample No.
Sampling Sites

Data Analysis
The values of determined heavy metals i.e.Iron, Copper, Nickel, Cobalt, Cadmium, lead, Mercury, Zinc and Chromium have been mentioned in tables 1 and 2

RESULTS and DISCUSSION
Studies for determining some important heavy metals like Fe, Cu, Ni, Co, Cd, Pb, Hg, Zn and Cr in under ground water, collected before and after rainwater harvesting, performed using Atomic Absorption Spectroscopy and their amounts have been reported in (parts per billion) ppb.Using the same method, studies were also conducted for a

Conclusion
The studies, which have been performed on heavy metals for various samples of water collected before and after monsoon, show that the values of heavy metals for almost all the samples have been decreased appreciably due to the mixing of rain water to the under ground water.Thus these parameters indicate that rainwater harvesting suitably affects the quality of ground water.And rainwater harvesting has proved its utility for the above-mentioned sites.
. Fig Nos. 1, 2, 3, 4, 5 and 6 show the graphical representation of the values of above mentioned heavy metals for the samples examined before and after monsoon.In the said figures X and Y specify the pre and post monsoon values and GV points out the guideline values prescribed by the World Health Organization.Additionally, Fig. -7 comprises the map depicting the study sites.
.No. & R.W. indicate the sample number and rain water respectively.