Electrolyte water can save lives, both human and animal. However, keep in mind dogs only need it when they're ill or injured--not after exercise or in hot weather.
When Dogs Need It
A dog may need electrolyte replacement when he's dehydrated from diarrhea or blood loss. A wound that bleeds heavily is a true emergency, while bloodsuckers on the outside, such as fleas and ticks, or on the inside, such as hookworms and tapeworms, are a long-term problem that can precipitate an equally urgent crisis. Either way, the dog needs immediate help to restore the content and balance of sodium and chloride in his bloodstream.
When Dogs Don’t Need It
A dog doesn't need electrolyte replacement when he's been exercising, even exercising very hard. When humans sweat to cool themselves, they lose salt (sodium chloride) and other minerals in their sweat. Since dogs don't sweat through their skin, they cool themselves by panting, which evaporates only water from their tongues. They don't lose any minerals this way and need only water replacement, without the electrolytes.
Store-bought Versus Homemade
Commercial electrolyte-balancing solutions for dogs are readily available through veterinarians and even on the Internet, but these may contain things a dog doesn't really need, mainly preservatives to keep them shelf-stable. With homemade electrolyte water, he can get the essential ingredients without anything he might be sensitive to.
Make Your Own
We've all heard the saying, "If a little bit's good, then a whole lot must be better," and this is true for many things, but not for everything. Electrolyte water needs to be made in careful proportions so as not to give a dog too much of anything. Sodium and chloride are already in correct proportion in ordinary table salt, so one teaspoonful of table salt dissolved in a quart of clean, fresh water will create an electrolyte replacement appropriate for a dehydrated dog. This mixture contains all he really needs in an emergency, but adding a tablespoonful of sugar or honey may make it more palatable to him without doing any harm. You can open a can of good-quality low-sodium chicken broth and dilute it with two cans of water; this lowers the sodium content enough that it won't hurt the dog and he may be more willing to take it with this flavoring. The ultimate restorative for a sick or injured dog is homemade chicken stock made with chicken necks, backs and wingtips simmered slowly for eight hours or until the bones crumble, then strained and seasoned with kitchen herbs (parsley, sage, thyme and the like, but no onion or garlic) and a measured teaspoon of salt per quart. This has actual easily digested protein content and is attractive to dogs in smell and taste.