As I am gulping down my calcium/magnesium tablets as I type, I wanted to note to others who read this who may head on for shopping for supplements that if you get 10 minutes of sunlight every day, you manufacture enough Vitamin D. Most supplements I see have calcium/magnesium but not always Vitamin D.
In Europe, I believe most pharmacies stock Polase brand (magnesium/potassium) electrolytes, and even better is Almora which is a more complete electrolyte water soluble powder. It will save your life if you live in hot weather or if you have stomach flu. I have been dehydrated many times in my life and I learned my lesson. In the US, Pedialyte is recommended for mild to moderate dehydration. Some supermarkets now also stock fresh coconut water (not milk) either as a fresh coconut or in a juice package or can. The fresh coconut tastes best and is natures natural electrolyte keeper, but the packaged stuff is acceptable too.
As with all supplements, don't overdo it. Too much calcium, magnesium, potassium and salt will do all kinds of bad and dangerous things to you: heart problems, blood pressure problems, bloating, diarrhea, etc. You should adjust accordingly. One glass per day with the daily dosage for a thalassemic is normal. An extra glass because you exercised or had diarrhea, or the weather is hot, is also acceptable. You replenish as you lose.