For the needs of your project, I think pond maintenance strips would work. You can buy them to test different levels of chemicals and nutrients in the water of a man-made pond. Try a garden store or bigger places like Ace or Wal-Mart. All of those will have them and can direct you to the best ones to use for your project.
Your science teacher may have some to give you, as well.
Your science teacher may have some to give you, as well.