More Discs

As Barry and John said this seems more like a first level, or the beginning levels of a game. Subsequently, we have (had already thought of this idea but got rid of it) thought of an freeze disc.
The player would receive this in the middle levels of the game.  They would use this when the player is possibly in a hotter cave system, they would freeze the water to help them reach platforms, freeze a waterfall to climb up it, if a cave has water running into it you can freeze the exit which will make the water level rise allowing the player to escape.

Another element to the freeze discs are that when dropped, an area the same size as the heat will be frozen, they can be picked up again and reused.  Since, the character is now in a hot climate the frozen platform will only stay for a certain amount of time.  This allows the player to not have to use as many discs.

The freeze discs can be used to freeze fire, which turns them into ice crystals (hurting the player), but this only lasts for a certain amount of time as the fire begins to melt the ice.  One scenario could be that there is so much fire the player can not get by so they freeze the flames allowing them to get by.

Scenarios for both Heat and Freeze discs:
There is a crack in the wall with water trickling in.  The player freezes the water, then uses a heat disc to melt the ice thus cracking the wall.  This can be used to escape and add more water to the room.

Similar to the two room puzzle with the heat discs.  But to stop the water running back into the first chamber you must re-freeze the whole.

Another Discs: Water
The player is in a room with no water and there is a plateau in front of them, the chamber is divided in two with a wall.  The player throws down a water disc then freezes the water to get across. When they can go back into the water to travel further into the cave system.

There is a crack in the ground but no water.  Use water disc, freeze then unfreeze to break through the wall.

The player using a couple of water disc to create a body of water (waterfall), the player can freeze this and then climb down the cliff into the chamber.

The player is in a long tunnel, they use the water disc which create a trickle of water.  the player freezes this and hops on and begin to slide quickly down the tunnel and must avoid ice crystal along the way.  If the player has no water discs they can melt and ice crystal thusly creating a trickle of water.

Water can be used to douse flames.

The player enters a room and the only exit is through a big chunk of ice which is cover in oil.  The player must use a heat discs which melts the ice but puts the oil on fire, then the player freeze the fire and had a limited time of going through.  This is not done underwater.  The player may think they can use a water disc but they cannot.

Multi Ways of solving
There are pillars above a body of water, the player can melt them and this will rise the water level allowing them to get out.  They may also use water discs but they will have to use alot.