I have only heard of dehydration lowering blood pressure, myself. I know that people with low blood pressure are asked to drink more water to raise it so I would be surprised if dehydration raised blood pressure. Of course, in the case of more serious dehydration, the heart might try to pump harder to get enough water to all the cells. This could increase blood pressure. Also if the concentrations of waste in the blood were higher from dehydration, this could also make the heart pump harder to try to get the material filtered our faster by the kidneys. I am curious so if you find the answer, please post it.