Water Piano Drive

This concept is for the grim future when oil supply are depleted or otherwise inaccesible. It is titled the Water Piano Drive, and is an excellent method of personal transportation across waterways or bodies of water. The basic method is to play a real song on an imaginary piano on the surface of the water. One would be propelled to a destination, fixed in one's mind prior to the commencement of performing the song, at a rate depending on two factors:
1. The accuracy with which the piece is played. This includes the originally perscribed tempo. For each mistake made, flourish failed, or beat-per-minute of tempo off, the user travels more slowly.
2. How much the deity which operates the WPD (with many ears and sub-net mental IPs) enjoys the piece being played. Be warned that he mostly likes Baroque music. So every time you make a mistake, it also displeases him, so he turns your speed knob down a little. This is an analog process, though one will invariably make a pun about the process's "digital" nature. This displeases the WPD deity.
This is a naturally occurring phenomenon involving zero-point energy and harpsicordian control volumes. Direction is determined by desired destination, as held in the user's mind, but it is cemented upon his departure.
If the piece finishes before the user has reached his destination, one does not, as one might presume, sink into the depths. Instead, since one is making the worst "mistake" one could by not playing anymore, one's speed actually slows down to the point of reversal, and the user is pulled quickly back to his point of origin. This cannot be reversed once started. Only one song may be used for trip, also.
It should also be noted that any one piece can only be being used for travel by one person at a time. To prevent everyone from picking much longer keyboard pieces for every little 2 mile trip, the United Nations has formed a committee that delegates what songs are appropriate for different ranges of trip length. The Water-Piano Relay League (WPRL) releases lists that are published in any port and available for purchase for modest rates in a nice, laminated, spiral-bound booklet. Furthermore, collections of the sheet music can be purchased, either individually or by trip length category, from the WPRL at minimal prices.