Denying patients food or water with intent to kill them is wrong
"By including artificially provided food and fluids within the category of treatment that a competent adult may decline, the 1992 Washington State Legislature passed a law that put food and fluids within the category of medical treatment that a legal guardian or surrogate may decline for incompetent patients who have not "executed an advance directive," or legally told the doctors how they want to be treated at the end of their life."
Please note in the above the absence of a requirement that the patient left instructions. Your state may also have a similar law in effect. Check with your local pro-life group.
The link also has an impressive list of symptoms experienced by those who are dehydrated to death. Do share when you have the chance. :-)