Why pure water is a bad conductor of electricity?

Answer 1

Because Pure water had very few ions; which are needed to conduct the electricity itself. While dirty water or salt water is a great conductor, because it has many other elements fused into the water making this kind of water a solution.

Answer 2

Water does not conduct electricity. It is the impurities (ions) that allow water to conduct electricity
Pure water is 'bad' conductor of electricity. As there are 'no' free electrons there to carry electricity forward. As hydrogen has 'shared' the only electron with oxygen atom, it has 'relative' positive charge. Hydrogen does not 'donate' electron to oxygen, though it 'demands' electron from hydrogen. Otherwise hydrogen will get 'net' positive charge. So water becomes one of the most polar molecule. And so it forms 'Hydrogen bond' with other molecules. Once you add salts like sodium and potassium chloride to it, which are fully ionized, it becomes very good conductor of electricity. Now question arises 'Why sodium and potassium get 100 % ionized'. For that you see the electronic configuration of them. Sodium has 2,8,1 and potassium has 2,8,8,1. Chlorine has 2,8,7. So sodium and potassium wants to 'give' extra electron to other atoms so that there 'octate' is full filled. By giving this 'extra electron', They both have 10 and 18 electron in hand. So 'net' loss of 'about' 10 % to 5 % electrical charge only respectively. Chlorine want extra electron to full fill outer orbit. For it, it is 'net' gain of 'about' 10 % electrical charge only. In case of hydrogen to give electron is 100 % loss or gain of electrical charge, so it has to thinks twice before giving or taking electron. So it 'shares' electron with other hydrogen atom. So both have 2 electrons in there outer orbit. It is the oxygen,chlorine atom whoforcibly try to take away electron from hydrogen atom to complete there 'octate'.