If I directly touch a live 220 volts wire (standard mains supply in India), then I will get electric shock. But, let's suppose, if I insert one mega ohms resistor in series between my hand and the 220 volts wire, then is there any chance of getting an electric shock. Theoretically, I guess the current cannot be more than about 0.22 milliamperes. But, I am worried about resistor malfunction due to overheating or some other problem like that which I may have overlooked. I plan to use this method in a product where a "sensor-wire" is inserted in a water tank and even if by any chance the "sensor-wire" comes in contact with a 220 volts wire, the "one mega ohms resistor" will act like a safety device so that no person who touches the water will ever get any shock under any circumstances. I understand that a better way would be to totally isolate (may be by opto-coupling? ) the "sensor-wire" from the high-voltage-circuitry, but as that might increase the cost of my products, I am thinking is it enough to just use a one mega resistor as a safety device. Any Suggestions?