I was thinking that relying on thirst when dry fasting is a bad idea, as what happens if the thirst trigger gets confused but you really do need to drink or you will die.

 http://vodalechit.narod.ru/o_r_d/glava1-1.htm

The above link (in Russian) is a very interesting article on the subject, I've copied and pasted the most important bits below:

Strictly speaking, the feeling of dryness in the mouth - this is not an indication on which to rely. The body can suffer from severe dehydration within the cells, but did not report this with the help of dryness in the mouth.

A clear indicator of dehydration is urine color. If the urine is always very fair, almost colorless, the body can be considered lucky, because he gets enough free water and can easily get rid of toxic waste. If the urine becomes stable natural yellow color - not from pigments derived from food, such as, for example, vitamins, and - this means that the body begins to experience a lack of free water.

Kidneys have to put more effort to get the toxic waste of food metabolism. Continuing orange urine - a sure sign of serious problems associated with severe dehydration. If these problems have not yet become apparent, then, the trouble is manifested in the very near future, possibly in the form of severe angina, stroke or even sudden death from a massive heart attack.

I think this explains why you should drink distilled water in your normal life:

Another group of researchers led by Dr. Bruce found that between the ages of 20 and 70 years, the ratio of water inside the cells to the amount of water outside the cells has changed radically - from 1,1 to 0,8. This means that the water around the cell becomes greater than inside, and by 70 years similar to plums cells begin to look more like prunes. Without a doubt, this is a pronounced change in the intracellular water balance, contributing to the emergence of various diseases can be avoided if you regularly drink water in an amount which will provide free water penetration through cell membranes throughout the body. Penetration or diffusion of water across the cell membrane normally goes at a speed of 0.03 cm per second. Indeed, very quickly, but it can be done only unbound or free, water. Water, which already osmotically bound to other elements to pass through the cell membrane can not.

SO MAYBE THE BEST INDICATOR OF BREAKING THE DRY FAST IS ONCE YOUR URINE TURNS ORANGE (mine did on my last 3 day fast, but this time it is still only a bit yellow)

comments welcome...