As a part of an exchange semester in Spiel und Lern Design at Burg Giebichenstein, Halle - Germany, I took up the course of playground design for a kindergarten.
Sand pits are a common sight in Germany though sans water. Children could often be seen carrying water bottles to play with sand. My design focussed on the same via a structure which dispenses water at different height levels. The form is such that it serves the purpose of slide as well. 
Also, to encourage sensory simulation - there are small islands underneath the sand for tactile exploration.