For those concerned with hydration and feeding tubes, there is a wonderful organization that is for the support of people on either feeding tubes or TPN dependency. Their link is
http://www.oley.org/ (I am a regional coordinator for my part of the country for this group, and I can honestly say that they have very good information, and for long termers they have regular conferences where you can get good information as well as get together with others who use the same "appliances" to feed.
Anyway, there is an excellent article in their most recent newsletter about oral (or gt) rehydration solutions, link is
http://www.oley.org/lifeline/ORS%20Article%20-%20Dr.%20Kelly.pdf My last link is a page of recipe's with several different ways to make an ORS (oral rehydration solution) at home, though not quite as accurate as the packets you can purchase (we get ours from our home care with the exact WHO formula in it) they are reasonable substitues...
http://www.rehydrate.org/solutions/homemade.htm hope this helps a little!
Heidi (Mom to the bravest boy I know, and daughter in law the bravest woman I know...)