I can't be sure my answers are the exact words, but it should be something along the lines of...
The amount of water on Earth is constant, but the form and location of the water changes as it moves through the water cycle.
This means that Earth has always had the same amount of water within in, along with it being the same water the whole time. No new water was introduced to our planet. Some of our water is liquid, some is solid, and some is gas. Some is deep in the soil and some is high up in the atmosphere. Some is in rain and some is in snow.
The first shell can hold up to 2 electrons, the second shell can hold up to 8 (2 + 6) electrons, the third shell can hold up to 18 (2 + 6 + 10) and so on.
