How does your submission match the theme?
Many of the mechanics in Guard 'N' Hose serve mutlpile purposes.
-The player's jump can be used to get above enemies, and then held to spray them with water.
-This water spray can be used to damage enemies and to clear dangerous slime from the ground, to create a safe place to land.
-This also lets the player hover, allowing for more dexterous aerial maneuvers.
-It can be used to bounce on round enemies to get above tall enemies, and regain some water while in the air.
-...And when landing, the player performs a Splash attack that damages all nearby enemies, as well as refilling all of the player's water.

I also took care to design orthogonal enemies as well, that encourage specific types of play.

I do regret how similar my concept ended up becoming to Downwell, though I believe it occupies a more defensive style of gameplay as opposed to the Downwell's combo-chasing offense.

Third-party resources
I used the Unity Engine to create this game.

Within Unity, I used iTween (free resource with open commercial license) link: http://www.pixelplacement.com/itween/index.php

And I used a song from Incompetech.com which is properly licensed in Guard 'N' Hose's title screen and the Contributors section below.

Contributors
Apart from my content, the only external contributor is Kevin Mcaleod, whose song I used. Here is the license:

Nowhere Land Kevin MacLeod (incompetech.com)
Licensed under Creative Commons: By Attribution 3.0 License
http://creativecommons.org/licenses/by/3.0/