EVERYONE has a different metabolism, sensitivity to heat and sunshine, and predisposition for heat or sunstroke. The hydration solution that is best, is the one that works for YOU.
Personally, I am a "stout" fellow. I also take several medications for chronic conditions that increases my sensitivity to sun, heat humidity, and exertion in warm and humid weather. I have also done five Caminos. Over the years (five) I have adopted a hydration routine THAT WORKS FOR ME.
Each morning, I try to consume a banana or orange, and tote a second piece of these fruits with me for consumption later. These are two excellent sources of the blood salts one's system needs. As noted by Kitsambler above, only drinking water, for most folks, can produce "down-stream" problems.
Your organs, the largest of which is the skin, needs these salts metabolized in your blood as fuel for your organs, all of them. Simply feeding them plain water depletes the available blood salts over time, and can lead to organ malfunction or failure.
To supplement this intake, I carry a tube of Nuun sports tablets, the type WITHOUT caffeine in them. I buy them either online, or obtain them in a local running store. They cost about USD 7.00 for a tube of 10 tablets.
To get them into the narrow neck of the .5 liter water bottles I always use on Camino, I simply crack the tablets in half along the score line. One full tablet makes one half liter, or about 16 fluid ounces of electrolyte solution.
I find that one tube of tablets will last more than three weeks. Here is why.
I only use them on warm sunny days, when I assess that I have not consumed enough fresh fruit, or fresh squeezed orange juice, and when I further assess that I might have a problem in the near while.
I do NOT wait until I am feint to use the Nuun solution. I have learned to listen to the symptoms and to take precautionary action when needed. Some symptoms include that you:
- stopped sweating even though others are sweating profusely
- do not FEEL thirsty
- have stopped needing to urinate
- urinate, but your urine output is deep yellow or darker. Dark is relatively worse
- feel light-headed
- woke up face-down in the soil (I face planted three times in 2015)
I have learned from experience to force myself to consume at least half a liter of some liquid every 90 minutes, even if I do not feel thirsty. I add the Nuun tablets only if I assess a bout of heat or sun stroke / exhaustion coming on.
A viable alternative for the Nuun tablets if you are caught without, or simply need an electrolyte "pick me up" is a bottle of Aquarius or Powerade sports drink (similar to Gatorade in the US). They are available in a variety of flavors and I have seen them sugar free as well. I have found them in both Portugal and Spain in tiendas and supermercados.
I hope this helps.