It would be quite the trick to drain the oceans of all the water they contain in 1000 years. Please refer to this:

https://i.redd.it/7t81ljatuh8a1.jpg

Please repeat this, clapping your hands together with each word

We. Are. Not. Going. To. Run. Out. Of. Water. On. Earth.

However, FRESH WATER... that's a tricky one.

The most brute force way would be desalination, of which there are a few ways to do this (evaporative, osmotic, etc). All can be resource or energy expensive (evaporative can be done with either a huge solar still, if you have a handy desert climate, or by using energy to boil salt water and then allow fresh water to condense)

Both have the problem of what to do with the highly concentrated brine (if you don't mind killing local fish/destroying your local fishery, sure just dump it back into the ocean).

But lets say that, yes, somehow we have squandered 321,003,271 cubic miles of ocean, and we need water from somewhere else. The outer solar system is _loaded_ with water ice. Often in combination with Nitrogen, Carbon Dioxide/Monoxide, Cyanide (HCN), and other hydrocarbons in smaller amounts. Just bring a few comets in to the vicinity of Earth and that material could be mined. Just don't let the comets _hit_ the Earth--you will make no friends that way, no matter how thirsty they are.