If you have limited water, you probably don't want to always use it with the ORS. Have 1L of pure, unmixed water has some advantages over the ORS.

I can site personal experience... I gave myself heat exhaustion from working in the lawn on a hot and humid day. I was drinking water while working, but probably not enough. Well, got dizzy, naseous, chilled... Drinking a electrolyte type drink didn't agree with me. Sipping pure water over a period of time brought my system back under control.

Yes, it is important to replace lost salt/sugars on some occasions. Sometimes pure water if preferred tho.