A couple's like fire and water - they balance each other out." - "Opposites attract, like fire and water. One fuels the passion, the other cools things down." - "Relationships are like fire and water - they can either clash or complement each other." - "You could say couples are like fire and water - a little bit of both makes it work." You could also play with the idea of fire and water having different effects on each other, like: - "Fire needs water to simmer down, just like couples need understanding to calm their differences." - "When the fire gets too hot, the water's there to bring it back down to earth."