I wrote about this in response to a question from a reader. I recommended using stainless steel wire cloth to sift “play sand” so it will be of uniform size and therefore work in a slow sand water filter. This has turned out to be somewhat time consuming, however once you get the stainless steel wire cloth set up on a frame the sifting is actually quite easy. The most recent effort uses 30 mesh stainless steel wire cloth to separate out the coarse sand, and then 60 mesh to allow the silt and very fine sand to be removed, as it will fall through the 60 mesh openings leaving the larger grains to sit on top. This works very well and is much better than starting out with the 40 mesh. What is left is very close to .15 mm effective size sand. Washing the sand then is quite easy and does not require lots of water. Absolutely wear a dust mask if you do this when the sand is dry. The dust from any sand is very harmful. I am in the process of locating sand that does not have as much silt (dust). Possibly “masonry sand” ???? Masonry sand must be free of organic material and silt.
Here in the Seattle area, it was fairly easy to locate a source for the sand from a manufacturer who supplies sifted, pre-packaged, graded sand; but this is not always possible in all locations.