UV-based water filter.

The demands of filtering rain water are different from those of filtering municipal and river system water supplies that may include endocrine disrupting chemicals, pharmaceuticals, agrochemicals and industrial chemicals, and unprocessed human and animal waste water. Rain water on the other hand usually only needs to have: any pollutants in the sky, dust particles, tar on roofs, and any chemical products that may be used for anything upon/within the catchment surface filtered out.

## Types of filters

When choosing filters Look for:

• Flow rate through filter and effect on ending water pressure
• Which suspended solids and contaminants can it remove
• Sequence of different filters based on which solids and contaminants are removed
• Cost

Filter Sequence for Isla Urbana rainwater catchment systems: Not all of the following filters are used in every system. The majority of systems sole have the pleated sediment filter followed by the activated carbon filter. These two filters alone can help purify the water enough for domestic uses.

### Reverse Osmosis Filter

• Is great at filtering large molecules and ions from solutions by applying pressure on one side of a selectively permeable membrane. This process is the opposite of natural osmosis where water (or solvent) passes from the area of high solute concentration to the area of low solute concentration. The pure water (or solvent) moves to equalize the solute on both sides generating pressure called the osmotic pressure. Applying pressure on one side reverses this process and is thus called reverse osmosis.
• Reverse osmosis is a common filtering application used in purification of seawater into drinking water.
• Efficiency of filtration is dependent on the concentration of the solute, the pressure, and the rate of water.

### 20" Cellulose Filter

Removes dust from charcoal as well as many trace elements including: lead, mercury, arsenic, aluminum, iron, fluorine, nitrogen, potassium, chlorine, sulfur, and others. Usually made of high density cotton.

### Silver Ion Filter

• Silver ions have antibacterial properties by inhibiting both the growth of bacterial organisms and their signal transduction.[1]
• two plates of silver are inserted into water piping and charges are alternated across the two plates creating arcs where silver ions jump off into the water.

### Ceramic water filters

Small Clay-Sawdust Ceramic Filter

Ceramic water filters, pot filters, ceramic water purifiers or ceramic silver water filters are ceramics pots made from a mixture of clay and sawdust fired at a relatively low temperature.

The most well known example of their use for filtering water in the developing world comes from Potters for Peace, who have a process for mass producing such filters, which are also impregnated with silver to kill off harmful bacteria and viruses. Such mass produced filters are certainly not the only instance or possible way of obtaining ceramic clay filters, as the resources needed, clay, sawdust, and water, are available in most parts of the world, and the manufacturing process is relatively simple.