What should be placed over the sand media in a sand filter?

Placing untreated building paper over the sand media in a sand filter serves an important purpose in the filtration process. It acts as a barrier that helps to keep the sand media in place while allowing water to flow through it. This material is porous enough to permit the effluent to pass while preventing the displacement of the sand, which could lead to clogging or imbalances within the filter system.

Untreated building paper does not leach harmful chemicals or materials that could contaminate the filter or the surrounding environment, making it a safe choice. It also possesses a level of durability to endure natural elements, protecting the sand media from the effects of erosion or degradation over time.

Other materials, such as tar paper or plastic sheeting, are not suitable because they can create a non-permeable barrier that may obstruct the flow of water, leading to poor filtration and potential system failure. Concrete slabs, while sturdy, would also prevent the necessary passage of water and disrupt the intended function of the sand filter. These alternative options fail to fulfill the requirement of maintaining proper water movement and filtration, emphasizing the importance of selecting the appropriate covering, which, in this case, is untreated building paper.