From Fellrnr.com, Running tips
→Water in the Body
== Blisters and black toe nails ==
Dehydration reduces body weight, which can reduce the size of your feet. This in turn changes the fit of your shoes, causing blisters. Hyponatremia can cause swelling, which increases the size of your feet and can cause blisters. Both conditions can also increase the chance of black toe nails.
==Water in the Body<ref name="CLINC"/>==
Approximately 60% of the human body weight is water, though this varies primarily with body fat as adipose (fat) tissue contains a lower percentage of water. Total Body Water (TBW) can be divided up into
* Intracellular fluid (ICF) which is 40% of body weight
* Extracellular fluid (ECF) which is the other 20% of body weight
** plasma is 25% of ECF/5% body weight
** interstitial fluid which is 75% of ECF/15% of body weight, typically 11 Liters/22 pints.
==Symptoms of Dehydration<ref name="CLINC"/>==