How much water should I drink?
Ecstasy increases your body temperature and the reason why you should drink water when taking E is to avoid overheating and dehydration. Water is not an antidote to the chemical effects of ecstasy.
How much water you should drink depends on the context in which you are taking ecstasy. While E will tend to raise your temperature, particularly when the external ambient temperature is high, you are going to get hotter in some situations than in others.
There have been a few cases of people dying through drinking too much water, believing that it would stop the effects of the E (the best known example being the well-publicised death of Leah Betts). If too much water is drunk, too quickly, then the level of sodium in the blood becomes diluted. With too little sodium water gets lost into the fabric of body tissue, causing swelling. If the brain swells, pressure is put on the brain stem, which controls heart and breathing functions. This can be fatal.
The point to remember is that water is needed to replenish what has been lost. You will lose lots of fluids if you are dancing vigorously in hot conditions, but not so much if you are sitting around with friends at home.
If you are dancing for hours on end in a hot and sweaty club or party then you should aim to drink about a 500ml bottle of water every hour. You should also think about drinking 'isotonic drinks' which will replace the salts and minerals you will be losing through sweating, or at least trying to eat a salty snack such as crisps or peanuts. Sip rather than gulp drinks. Don't just rely on drinking water to cool you down - take breaks, go to the chill-out, splash some water on your face in the bathroom. Make sure you urinate, even if it's difficult.
As well as club situations, be aware of the need to drink enough water and not to get too hot if you are taking E outdoors on a sunny day (at a festival, for example) or if you are planning to take it somewhere where water might not be so easily available (such as hiking in the countryside).
The links between neurotoxicity and temperature have been well-researched. Stay cool to help yourself stay safe.