Jiju,
Okay, it sounds like you are describing something that people do -- adding coins to water with the belief that this will purify the water -- and you want to investigate whether this actually works or not. I can think of a few questions for you to investigate that will make the problem clearer:
1.
What are the coins actually made of? Historically, a lot of coins were made of pure precious metals. But lately those metals have become scarce and their value has gone up, so most coins are alloys rather than pure metal. These alloys usually hold up better over time as well. If the coins are not pure silver or pure copper, the other metals present could also be doing something, and the ability of silver/copper to be dissolved in water could also be different in this different state. I didn't find any resources that stated specifically what modern coins in India are made of, but you could start here:
http://en.wikipedia.org/wiki/Indian_coinage
http://www.rbi.org.in/currency/coins.html
2.
What mechanisms of purification are supposed to be at work? I'm not sure whether you're talking about antimicrobial properties or about removing other ions from the water, perhaps by forming insoluble compounds that precipitate. To remove other ions, either some silver/copper would have to be dissolved into the water, or you would see the removed impurities forming a film on the coins (unless the silver/copper was catalyzing some reaction between two types of contaminant ions, but that would depend on both being present). For antimicrobial properties, I don't think any silver/copper actually has to dissolve into the water: there are countertops, dish-drying racks, etc impregnated with silver that claim to have antimicrobial properties, and Wikipedia says that brass doorknobs are able to kill bacteria on their surfaces. As a starting point:
http://en.wikipedia.org/wiki/Silver#In_medicine
http://en.wikipedia.org/wiki/Copper#Germicidal_effect
http://en.wikipedia.org/wiki/Oligodynamic_effect
3.
Given the above answers, how can water be purified efficiently? This will depend on your answers to the first two questions. For example, if contact with the surface of coins is important, you might want to run a very shallow stream over a bed of coins, or do the exposure in batches with the water stirred thoroughly. You were wondering whether this would work well at "room condition" -- it might be worthwhile to see whether the process is more efficient at a higher temperature, since higher temperatures increase the rate of chemical processes. To do an experiment you would need to form a hypothesis regarding some aspect of this process, identify independent variable(s) to test this hypothesis, and do the same thing with a control (probably no coins). You would also need a way to measure the degree of purification.
Again, our primary focus is giving advice and resources to K-12 students for conducting science experiments, so if you can start developing your question into a science project, we can give the most help.
Amanda