Teague Labs wanted to answer the question "how much water we spent daily"? To answer, they had to build a precision water measuring system. So, they got a high precision water meter used for PC cooling systems, a mini Arduino Yellow Jacket with built in wireless module and a PC that records data. They installed the flow sensor on their kitchen faucet, and started recording data.
Taking it further, they installed a monitor to show data in real-time. Amazingly, they recorded human behavior change! Check out this video. The project can be found in this link.