Question

adding salt to distilled water makes it good or poor conductor

Answer 1

Distilled water is the pure form of water. It is neutral in nature and also it doesn't dissociate into ions and it has negligible ionization.

Electricity needs ions to move in an electrolyte, which is not provided by water.

Rain water on the other hand,contains dissolved salts, acids and even few basic particles. These particles dissociate in water into ions which help in conduction of electricity.

So, Rain water conduct electricity.

Answer 2

It makes it a good conductor of electricity because salt ( NaCl) get converted into ions and the flow of these ions make the distilled water conductive