Slow Sand Filtration

Slow sand filtration is a water treatment process that uses naturally occurring biological activity to clean drinking water. Slow sand filters have been in use for centuries, and are time-tested systems for cleaning drinking water.

Salem’s slow sand filtration facility is located on Geren Island in the North Santiam River. Water from the North Santiam River is processed on three large slow sand filters located on the island.

How Does Slow Sand Work?

1. Water from the North Santiam River is put onto large slow sand filters.

2. Algae, protozoa, and small invertebrates that live in the slow sand filter remove biological contaminants, such as Cryptosporidium. The surface of the slow sand filter is where most of the contaminant removal occurs.

3. Straining of dirt and clay particles occurs at the surface of the filter as well as further down through the sand and gravel.

4. After water passes through the slow sand filter, chlorine and fluoride are added before it is sent to your tap.