I'd guess the zdoom way for both is easy as hell
slopes: make two sectors one lower than the other (if you want the slope to go down, higher if you want it to go up, same way with ceiling) give it the line special 181(slope), 2 parmeters ceiling slope 1 for it to slope in front 2 to slope in back 3 to slope both, I think it sounds easy <!-- s:D --><img src="{SMILIES_PATH}/icon_biggrin.gif" alt=":D" title="Very Happy" /><!-- s:D -->
water: make a sector with floor fwater1 and tag it 1, make a dummy/control sector with a ceiling fwater1 but the ceiling has to be the same as the floor of the sector, give one of the lines in the control sector the line special, water or some shit you make up, and tag the line with the same tag as the tagged sector. Also easy <!-- s:D --><img src="{SMILIES_PATH}/icon_biggrin.gif" alt=":D" title="Very Happy" /><!-- s:D -->