My topic is to persuade my audience to drink enough water. But also need to be credible? How do I come off as credible?

Look up the dangers of dehydration. Explain the bad things that can happen, then list the symptoms. A lot of people will recognize the symptoms! Don't exaggerate, don't blame, don't talk down to your audience. Mention your sources (in a spoken presentation, mention them briefly, just to show that you're not making all this up).

Since my 50s when I get really dehydrated I get kidney stones. I've gotten 4 so far. They are EXTREMELY PAINFUL, in fact it's said that kidney stones are the most painful thing a man can have (for women it's childbirth, though some women tell me it wasn't that bad. In fact they say women can handle pain better than men just BECAUSE of childbirth!) Anyway, anyone who's ever had a kidney stone will listen to you! 8^)

You can't if you are a regular high school student.

credibility normally = a Dr., a PhD , a nurse for that subject

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