"Fasting" a word for going without food, what is the equivalent for going without water?

Solution 1:

The OP asked

Does English have a word for voluntarily abstaining from water, like "fasting" for voluntarily abstaining from food?

If a person eats food but does not drink any fluids, they are still consuming water in the foods they eat; fruit, vegetables, and some meats have a very high water content. (source)

If the person voluntarily abstains from eating food and drinking any fluids, that is within the definition of fasting.

Fasting

Fasting is primarily the act of willingly abstaining from some or all food, drink, or both, for a period of time. A fast may be total or partial concerning that from which one fasts, and may be prolonged or intermittent as to the period of fasting.

Wikipedia, Abstinence

As the term fasting is a fairly broad term, a more precise expression that describes abstaining from all food and fluids (including water) would be an absolute fast or dry fasting, or ta'anit (a Hebrew fast).

If someone refuses to eat for political or personal reasons that is a “hunger strike”; this form of protest may also include the refusal to drink fluids.