For ordinary drinking during a normal hot day, plain water is a sensible starting point. Keeping water available and taking breaks from the heat also matter. Electrolyte drinks vary in what they contain and the situations for which they are sold.
Think about what the day involves
A walk from the station to the office and a long outdoor sports session ask different things of you. For the first, think about carrying water and finding a place to cool off. For sustained strenuous activity, ask for guidance suited to the conditions and your health needs. If you have been given a fluid or sodium limit, follow your care plan.
Read the bottle before comparing it
Look at the intended use, serving size, sugars and sodium. Put two drinks on the same basis, such as per 100 ml, and then consider how much of each you expect to drink. A vitamin tablet that fizzes in water is a different type of product from oral rehydration salts, which have specific uses and preparation directions.
Pay attention to how you feel
When someone feels significantly unwell in the heat, move to a cooler place and seek appropriate help. Confusion or collapse in heat calls for urgent medical care. For everyday routines, see the hydration and tiredness guide. The effervescent supplements and ORS comparison explains how to distinguish the categories.