To answer your question WetFeet a 737 will carry whatever bottled water it's current bar packing plan allows it to and is based on previous sales. It will not be enough for 200 people in a delay situation such as this.
Bottled water will not make much difference in a situation like this. At 45° or 50° C, passengers would have to be sitting in the middle of a windstorm in order to stay safely cooled by perspiration alone, and there was probably no air movement at all inside the cabin. Even with ventilation running, the air movement would be far too slow to help at all at these temperatures. At these temperatures, in fact, heatstroke is possible, and since heatstroke can cause brain damage in just a few minutes, this level of heat is a medical emergency rather than merely a comfort issue.
Since no one developed heatstroke, apparently, either the temperature was actually considerably lower, or they were extremely lucky. At 45° C, air conditioning is the only safe option.