Do saliva, water , oral sex kill sperm??

No — none of these things can kill sperm or prevent pregnancy. Pregnancy can happen anytime semen gets inside the vagina. If this has happened, saliva, water, or oral sex definitely won’t do anything to help prevent pregnancy.

If you want to avoid pregnancy, condoms are really effective at stopping sperm from entering the vagina during sex. If you’ve already had unprotected sex, you can take emergency contraception (also known as the morning-after pill or Plan B) within 5 days (or 120 hours) to prevent pregnancy. Even better? Using condoms along with a highly effective birth control method like the pill or the IUD.

Read more about how pregnancy happens here.