Surface Water Treatment by Roughing Filters - A Design, Construction and Operation Manual (SANDEC - SKAT, 1996, 180 p.): Part 1: General aspects of roughing filter application: 5. Bacteriological water quality improvement: 5.1 Slow sand filtration
water purification - How do slow sand filters work and are there any alternatives? - The Great Outdoors Stack Exchange
How to design a pressure sand filter? Pressure Sand Filter Calculator