Its Lets be clear upfront, we currently only have the water signature of one Jupiter family comet aka P67/Churyumov-Gerasimenko. (Jan-2015) Since the water signature is different from Earth's water, there are afew ways you can conclude: li Comets did not bring water to Earth li Asteroids brought water to Earth li Still too early to conclude what brought water to Earth li Earth was created from water in the beginning
Scientists are still having problems explaining why the Earth has so much water. Most however, believe that Earth was formed bottom up and Earth's water was delivered to us by Comets and/or Asteroids. It was interesting to read the different conclusion adopted by the various news headlines, but i think we are still far from a definite scientific answer. While the Bible favors Tidal Downsizing, as it clearly says the Earth was formed from water.