Lake Evian was one the first lakes that the kids in the Perdido Beach started to use for water. The kids used trucks to transport the water down and distribute between the population.
In Plague, Albert knew that there was near to no gas left to transport the water. He also knew something which no one else knew; the lake was drying up a lot quicker then the citizens of Perdido Beach thought. Due to theses factors, he sent Sam, Dekka, Computer Jack, and Taylor on a mission to try find Lake Tramonto.
Lake Evian is most likely a direct reference to the actual bottled water company Evian.