It's real. Snow is significantly less dense than liquid water, so for an identical mass of liquid water, the volume of equivalent snow mass will be much greater than the volume of water. The density, and thus the difference between the amount of snow and the equivalent amount of water (i.e., the snow water equivalent or SWE), is a function of temperature, e.g., this discussion. Generally, as temperature decreases, snow volume for the same SWE goes up, for example the graph on that page highlights that 1 inch (~2.5 cm) of rain can equal ~100 inches (~250 cm) of snow when the temperature is -40 to -21 F (-40 to -29 C) but would only equal ~10 inches (~25 cm) at 28 to 34 F (-2 to 1 C). Importantly, none of these are accounting for compaction of snow after it falls, where the density of snow can increase significantly with increasing accumulation.