Gravel in water filtration systems serves as a vital support and distribution layer, typically placed at the bottom of filter beds. Available in sizes ranging from 2mm to 50mm, gravel layers are strategically arranged with the largest particles at the bottom, gradually decreasing in size toward the top. This graduated layering prevents finer filter media from washing into the underdrain system while ensuring even water distribution during both service and backwash cycles. A typical arrangement might include 25-50mm gravel at the base, followed by 12-25mm, then 6-12mm, and finally 2-6mm layers, with each layer's depth carefully calculated based on system requirements. The angular nature of crushed gravel provides stable bedding and prevents channeling, while rounded river gravel offers better flow distribution. Both materials must be highly durable and chemically inert to maintain long-term system integrity.