Need help with research/argument essay topic + thesis?

Ok, I have to do a 10 page research paper but I’m having trouble with a few issues and my teacher is too busy to really help or reply quickly!

I have to write about(this is what the Prof. wrote):
Issues concerning the future. Or possible issues concerning either the planet or humans. (with a focused narrow approach)

I want to write about water safety. With topics like toxins,dangers, potential terrorists use of the water. But when I emailed the teacher she said to be specific and just focus on one local area like Santa Monica Bay and that it should be an argument paper. So now I’m unsure what to write! what sort of thesis could I come up with to still fit the topic the teacher assigned?

Plus, the paper is broken down into parts so it’s easier:
4 papers, one each on:
Definition
cause and effect
values
policy
(about 2.5 pages each, put all together to make one paper)

So what type of stuff should I write to fill up the first essay(definition)?

(I got this assignment late, so if anyone knows of an easier topic I might want to consider, please let me know)