Rainwater prefilters are generally the first step in a rainwater harvesting system, rainwater prefilters are designed to clean the incoming rainwater of debris that came off the roof. Some prefilters require maintenance, while others are self cleaning.
Rainwater prefilters are designed to remove solid particles that contains bacteria, and other solid matter that can be found in the rainwater after hitting the collection surface. The prefilter will also aerate and ogygenate the water which will reduce the amount of bacteria. Aeration can also help oxidized dissolved metals like iron, which can then be easily removed.
First, the prefilter provides a first flush action. The initial rainfall, which is full of contaminants, is rinsed off the roof pass the filter mesh, flowing to the dirty water or storm discharge. As rainwater passes by the stainless steel vertical mesh, the mesh itself is coated in water. Once the mesh is completely coated with water, it begins to pull rainwater through the inner fine mesh to the outer coarser mesh through adhesion or surface tension. The water is directed to the rainwater tank. This process agitates the water and provides aeration. The downspout filter will filter out particles greater than 320 microns (0.32mm or 0.013”). The centralized filter will filter out particles greater than 280 microns (0.28 mm or 0.011”).
The mesh is constructed with stainless steel and never has to be replaced. Due to the vertical design of the mesh, they are virtually self cleaning. Hard rainfall will completely clean the mesh. General maintenance is required 2-4 times a year, and is achieved simply by removing the filter and rinsing it clean with water.
The prefilter should never backup, as the system water can leave through two discharge points: the filtered water outlet to the tank; or the dirty water discharge to grade, storm system, or other adequate location. Based on this design, the filter has a larger pipe volume leaving than entering the filter. This filter can act as a secondary overflow point.