As the world's population increases, clean water is becoming a scarcity. It has often been cited as the 'Next Oil'. If history is any indication (and it often is), wars over water are inevitable unless actions are taken.
The word 'WAR' is placed over the existing slogan 'Water is life'. It's bold, all caps and is made to simulate the absorption of blood. It is intended to shock with a strange and uneasy colour palette (normally the blood would be red and the water would be blue).
Transparency is used so both slogans can be read over top of each other. From far the poster can also be read as 'Water war'.