Proposal
Runners and bikers often spend long periods of time covering long distances. A lot of times we they are out for so long that they would run out of water if they didn't plan in advance.
However, planning is not always possible because runners and bikers might take different, unfamiliar routes to make things interesting or simply be in a new area where they're not familiar with the locations of water sources. Our TUI implementation would be a set of water bottles that could sense the amount of water you have with you and your proximity to a nearby water source. If the system thinks you should fill up (maybe after this water source the next one isn't for another 20 miles) there would be some sort of feedback in the water bottles themselves. Maybe they would glow a color, vibrate or make a noise. This would overcome several issues that simply carrying a location aware device cannot do on its own.
1) Runners and bikers try to minimize the amount of gear they carry with them but they will always have water bottles with them. Thus it is advantageous to not have to carry yet another device, like GPS, in order to help you find water.
2) It can be dangerous and distracting to have a technology like GPS be in your foreground, consuming your attention when doing things like biking or running at a high speed. I would much rather my water bottle inform me that it needs to be and can be refiled nearby by glowing than by having a cell phone or GPS device start to beep at me, requiring I interact with it to find out some specific information.
3) This sort of information could also be used in survival situations. One could imagine a scenario where, when lost, a skier or mountain biker could activate the system and it would direct them to a water source. This assumes they do not have a more robust GPS system with them.
Our idea is inspired partially by our own needs, but also by Tod Kurt's ideas regarding wearable devices that inform you about your environment.
Materials
Several water bottles
Several led lights
One Ardunio board
One GPS locating device