Water of course has the fluid you need because that's what it is; just fluid. The potential drawback however is that once you start training and racing and drinking lots of water, your body starts using some of that fluid (in muscle contractions and for cooling for example) and gets rid of the rest through a few different mechanisms such as urination because the body can store and use only so much pure water. Therein lies the problem: the more straight water you drink the more you lose.
That's where electrolytes such as sodium and potassium come in. By their very nature they help your body retain the fluid it needs to function properly. Drinks with electrolytes are so important for proper hydration as they act as a catalyst to help your body retain fluid necessary for muscles to work properly so you don't lose all that valuable fluid. GU Brew Electrolyte Tablets are fortified with a unique blend of electrolytes, making them a better form of hydrating than water alone. So where you may typically grab a bottle of just water, you can retain the fluid you need to stay hydrated. GU Electrolyte Tablets are perfect for rehydrating on the go, whilst packets are great for keeping at home and work.
GU Brew can be used with other GU products as part of an athlete's nutrition regime. An athlete using GU Brew Electrolyte Tablets should account for the lower calorie intake than GU Brew Packets and possibly add an extra GU Energy Gel, Roctane or a Serving of Chomps (all roughly 100 calories).