A-rank water vs A-rank fire : Water puts it out and continues.
S-rank water vs A-rank fire : Same as above.
A-rank water vs S rank fire : Both jutsus cancel each other out and steam is created.
Fire - Water = Steam, a good way to conceal yourself, the fire heats the water up and thereby turns it into steam. The Steam itself can't be used as an attack, (exception - Han) but it's a great way to confuse your opponent.
Wind - Water = Faster water, but apart from that, nothing really, maybe you could use it to spread your water more, or make some cool tornados, but jutsus like that already exists.
Lightning - Water = Electric water, often used a brilliant combo, but it can backfire on you really bad, if you touch the water you loose the fight.
Earth - Water = Mud, good at immobilizing your opponent, and even blinding him, but unless you harden it with fire, it isn't exactly lethal or anything.
Okay, Read this Carefully, This could be very handy trough a battle (It always Help's me so Save this in a Document)