I don't know that there's been any kind of study into that. I know that anytime a non-waterborne virus is diluted it becomes weaker so it stands to reason HIV would have a lower viral load in water but as long as it remains inside of it's environmental conditions and can continue to find healthy bloodcels to infect it can remain alive indefinately.
To wolf I ask that question because my daughter drank from a person with aids and I was wondering if the person mouth was bleeding and blood got in the water and my daughter had custs in her mouth would she be infected.
Like I said the viral load of infected blood diluted with water would be low. If someone HIV positive drank from a glass the amount of the virus in the backwash with a minor cut would be so insignificant it would be difficult to measure, then that is further diluted into the rest of the water. If your daughter drank every drop left in the glass and licked the glass clean the exposure would be so insignificant that it would be almost impossible for her to contract the virus. More likely than not she had no contact with the virus. I think she's perfectly fine.