Q: If a man's penis or a woman's vagina comes in contact with HIV infected seminal discharge of a third person in a swimming pool can it infected the man and woman who are uninfected earlier?

A:Most unlikely, even if semen was to be discharged in a swimming pool, the dilution would be such that the chances of infection to another person seems very very remote. Besides most swimming pools are heavily chlorinated and even this 2% chlorine would eventually kill any HIV on contact. Stop worrying, enjoy swimming.