el nadador del sol said:
"Or even drink a little rusty water to get your daily iron supplement for free!"

This made me laugh! Thank you!
I was being a little frivolous. It's the nature of the beast, I am afraid
Last summer I also used re-hydration salts on my camino on the Le Puy route. But I made my own to save money. There are numerous recipes on the web. Have a look at:
http://rehydrate.org/solutions/homemade.htm
My recipe was 1tspn of "low sodium" salt, 6 tspns of sugar, 1 litre of water. That might sound horrible to taste, but it was actually slightly sweetish and not bad at all to drink.
Low sodium salt is available in large supermarkets (at least in Australia). It is simply salt with potassium chloride as well as sodium chloride. Potassium is important to cell metabolism.
I used sugar, but glucose would be better if available cheaply from health stores.
Every morning I filled my two 500ml bottles and added the salt/sugar mixture. When that water ran out, I just drank normal water. I did try to make one of the bottles last through the day.
Making your own saves a lot of money, Those commercial salts are quite expensive and their extra ingredients are useful, but not essential for moderate intensity activity - despite all the impressive advertising. Sure, if you are performing at peak intensity in some elite sport or marathon you need magnesium and all that other stuff you see on the labels.
Bob M