Killing yourself should never be an option. Live on in spite of any hardship instead of ever giving in.
On topic, suicide by dehydration wouldn't be moderate suffering, it would be completely and entirely miserable.. dry mouth, dry throat, stomach pains/cramps.. lack of sleep due to those ailments.. weakness, fatigue.. It would literally take more time than just a few days.. The body would deplete your fat reserves and then muscle tissue.. unless your rain dried up first and started to hemorrhage.. Terrible, just terrible.