Does Cold water kill diseases std germs bacteria?

No, but no worries. Cold water just washes them away. If they are hardy enough to survive in cold water, then they don't die in the cold water. However, many germs do not have cold water as their natural habitat, so they eventually die if left in the cold water. Washing with cold water is cleaner than not washing at all. Sometimes, people don't have hot water, but still can live normal lives with cold water.