Switches activate devices when they themselves are activated with any type of Fluid.
Once it is activated, it and the device connected to it stays in its new state.
Multiple switches can appear on a level, but no more than four will appear which are split into different colors with different symbols. Red has a gear, blue has a diamond, green has a reticle-like gear and purple has a hexagon.
Depending on the number of switches in a level, the colors will appear in either the order Red-Blue-Green-Purple or Red-Green-Blue-Purple. However, some levels break the rule:
In one of the levels in Where's My Water? Free, (Meet Swampy level 1-6 Crack The Code) has red, blue and purple.