Do a speech about the dangerous health effects of unclean water.
Make a video about the topic, but be sure to make it engaging and entertaining, while still factual of course. The goal is to keep the audience awake and remembering the message.
Post fliers around the school campus that has both text and images about polluted water
Go up to several people with a water bottle filled with polluted water, asking people "would you drink this?". The answer they likely would say is "no" and that might help them remember rater than a flier that they might overlook.
Go on the local news to talk about this issue. An alternative is to buy ad time on tv. To be fair, a lot of people are getting their news online so buying internet advertisement might be more effective.
If you don't have much of a budget to buy ad time, then you can post about it on social media and spread the word with your friends.
There are probably other better ideas out there but those are ones that came to mind.
