Diseases in Public Swimming Pool!?...but how would...?

Useless bckgrnd info (real question after line skip): I'm taking beginning swim at school, and failing miserably (slow learner. can't kick right. can't do side swim thing). so I decided, "okay, nearby public swimming pool, 3 hours a day till i get it!" and off i went. went today. learned a little bit (still have trouble. try again tomorrow). but then my mom comes and say, "you cannot go back there ever again! there are diseases there and you could get AIDS or some other virus and then it won't be worth it to die just to practice there! Promise me you will never go there again!!" --- still going there anyway, but now i'm curious (and need this info to justify by blatant disobedience!):

I understand how there would be diseases in a pool with a couple hundred people in it, but HOW would, say, a virus resistant to the disinfectant end up in the body?? (would it be ONLY through open sores, or somehow through accessory sex organs *swims to it?* or through digestive tract *survives acid!?*

There are bugs you can get from public swimming pools, but HIV isn't one of them. Ever.

The most common bug is tinea (athlete's foot) from the shower. People sometimes get mild eye or ear infections or sometimes stomach upsets from the water, but this shouldn't happen often if they chlorinate the water properly, and you avoid swallowing too much of it. Make sure you dry your feet and ears properly, and wear goggles if you're putting your head underwater.

You are extremely unlikely to catch anything serious from a properly maintained public pool. You are much more likely to die from drowning if you haven't learned to swim. Being able to swim well is an excellent skill to have and great exercise. Keep practising, although you probably need to keep working on convincing your mom.

Chlorine pretty much kills everything. Don't worry.

Interesting concept, but if the pool is well chlorinated, the diseases would not survive. the whole reason water in a pool is chlorinated is to protect it from diseases from the swimmers or etc.

If the pool is maintained properly, there are no diseases in it.
How would a school monitor the health of all of their students, and why does your mother think their pool is so much cleaner?

This if from an HIV website:

Can I share a toilet with someone who has AIDS?
Definitely.
You cannot get an HIV infection from a toilet, public or private, clean or dirty. The AIDS virus does not survive outside bodily fluids or in the open for very long. Similarly, you cannot be infected with HIV by swimming in a public pool, sharing utensils or clothes, eating from the same dish or engaging in normal social interaction with an infected person.

See the link below for the website. This question was addressed about halfway down.
Best wishes.