How did water become so abundant on our planet?

It is implausible that Earth's water originated only from comets, since isotope measurements of the deuterium to hydrogen (D/H) ratio in comets Halley, Hyakutake, Hale-Bopp, 2002T7, and Tuttle, yield values approximately twice that of oceanic water.

There are many theories that when a meter came to earth that it brought water. Scientist say that there were many meteors that hit until there was finally the perfect liquid for living organisms to drink. This happened a very long time ago but scientists were able to find proof of meteors in our oceans, rivers, lakes etc. Luckily there is a system we humans use to clean water.