The amount of water snow contains can very greatly, depending upon the snow.
Gather a set amount of snow... I collected approximately 500 ml of snow.
Allow the snow to melt - if you'll be allowing it to sit for an extended time, you may wish to cover it to minimize the amount lost to evaporation.
My 500 ml of snow yielded slightly less than 50 ml of water. This was a very dry, powdery snow.
If you live in a place that gets snow throughout the winter, you might want to repeat this activity with each snowfall and see how they vary in water content.
You may also want to measure the pH of the snow water.