Well with all the heat at the mo it usually gets people asking me how much water they should put away. Theres no need to emphasise the benefits here as I'm sure you all know them.
The body can just about cope with processing 1 litre per hour comfortably without major effect upon cells. In a day I usually aim to get through 2-3litres depending on what I'm doing. Adding cordial to water helps you take on more water. Basically you body deals with the glucose being seperated from the water as opposed to simple hydrogen and oxygen that are dispatched with more easily. This allows more time to process the water.
I just thought I'd share a couple of examples of simple hydration tests I have come by in the past.
The first is to weigh yourself before training and after. then using the difference as a level of liquid lost. Not really that applicable to a gym session but if you are off out to do some cardio for 2 hours maybe worth considering.
The second, and not for the faint hearted, is to micturate (medical term to take a piss) into a clear plastic bottle. Then to study the colour and smell.
Obviously the less the fragrance and clearer the colour the better hydrated. There are several factors affecting this but its ok as a baseline indicator. Women may need a funnel. Its a common test used in the military in hot climates.