No supplement is an alternative to varied and balanced diet and adequate consumption of water.
But during heavy physical work, exercise or during any sport events, if you are sweating and when you feel tired or low, you need to replenish yourself.
In summers, when the fluid loss is heavy through sweat even for normal physical load, then one can replenish daily
In certain geographical areas where sweating is a part of the climatic conditions, when you tend to loose water through sweat and heat, then you can replenish as and when required