Water treatment devices that include filtration media with specified grain size distributions are provided. In one arrangement, the device contains a volume of grains such that between about 1 and 15 vol % of the grains have a grain size in a range between a first grain size and a second grain size, a first portion of the grains have grain sizes smaller than the first grain size, and a second portion of the grains have grain sizes larger than the second grain size. The first grain size can be between about 50 and 100 μm and the second grain size can be between about 100 and 150 μm. In other arrangements, the first grain size can be between about 70 and 90 μm and the second grain size can be between about 100 and 130 μm. The difference between the first grain size and the second grain size can be at least 20 μm. In other arrangements, the difference between the first grain size and the second grain size can be at least 10 μm.