Blue water Veteran has to do with The Blue Water Navy Vietnam Veterans Act of 2019. Signed into low on June 25, 2019, it went in to effect January 1 2020. The law states that Veterans who server offshore of the Republic of Vietnam between January 9, 1962 and May 7, 1975, are presumed to have been exposed to herbicides such as Agent Orange and may be entitled to service connection for conditions related to that exposure. Some of the conditions that are presumed to have occurred secondary to Agent Orange exposure include:
Presumptive service connection means that veterans do not have to prove a medical nexus between their condition and their military service.
To be eligible for presumptive conditions, the Veteran must have served in the offshore waters of the Republic of Vietnam not more than 12-nautical miles seaward.
There are many sites online to check the location of your ship during active duty.