Simpler Water Level To the Editor: Regarding the article "Water Level Know-How" (Toolbox, 8/95): A third method of water-levelry is the two-person "very simple system" in which you make a mark on the wall at an appropriate level, give one end of the hose to a helper, go to wherever it is you want to level (with a thumb over the end of the hose), then raise or lower the end of the hose until your helper sings out "Yo! It's on the line!" You wait a few seconds to make sure the water has stopped moving, and mark it. Then you're off to the next location. Who cares if you spill a little water, because you