If you had a stream and a long length of hose pipe (garden hose would be ideal) you could submerge it completely in a coil in the water - bleeb out
all the air (you may have to get one end and suck a bit!) and then run that end down hill you will of set up a cyphen system.
Now you can just leave it there once that's set up - dig a hole in the ground a bit bigger and deeper so that the coil will fit nicely in - make sure
the up stream and the down stream ends of the pipe stay fixed in place (it is vital of course that the up stream one stays under the water!!! - if you
get too much air in that end the cyphen is ruined!!).
Fish your coil of hose out of the water - place it in your pit and voila! A fridge - the water will keep it at the constant temperature of the river
as the river water will always flow through the pipe - once set up it will in theory run indefinitely so long as the chphen system is not
compromised!!
Now I know your thinking you could just use the river! - well the advantages are things like you can maybe position this so it's hidden, a bit more
secure, bit more perminant, the food should not actually come into contact with the water... You could line the hole somehow for hygene AND ITS
IMPOSSIBLE FOR YOUR GRUB TO FLOAT AWAY
edit: actually I seem to remember someone one one of those science challenge shows for school kids was actually able to get heat from a cold river

... He made him self a hut away in the woods somewhere and invented things for it - but he used a variation of my hose pipe fridge above, but
the majority of the pipe was left in the river and he had a small part of it running through his hut - and his hut always stayed a little warmer than
his mates with no heating


- he said he was getting a slight amount of heat energy somehow, not sure I understand that one
[edit on 1/10/2009 by Now_Then]