| A reverse osmosis water purification unit could | | | | become ineffective. Chlorine must be used prior to |
| include a variety of steps. The necessary steps | | | | the thin membrane if bacteria and other biological |
| depend on the types of contaminants present. A | | | | contaminants are present. Otherwise, the |
| sediment filter will trap particles of rust or calcium. A | | | | contaminants will build up on the membranes creating |
| second sediment filter with smaller holes than the | | | | a dangerous situation. |
| first can be used to trap smaller particles. In some | | | | Waterborne illnesses are similar to food poisoning and |
| cases, a series of progressively smaller filters must | | | | are a serious threat to those with weakened immune |
| be used. If the filtration system was created for a | | | | systems. A reverse osmosis water purification unit |
| public treatment facility, the progression will stop at a | | | | alone does not provide protection against waterborne |
| point that will not interfere with the flow rate. The | | | | illnesses. There is one exception. Parasites called |
| flow rate can vary, as long as it is sufficient to meet | | | | cryptosporidium and giardia cause waterborne |
| the consumers' needs. A much lower flow rate is | | | | illnesses, too. The cysts or egg-like stage of |
| acceptable in a private home, which means that | | | | development is resistant to chlorine and other |
| smaller more effective filters can be used in units | | | | disinfectants. |
| designed for home use. | | | | They can only be filtered out, but in order to filter |
| Sediment filters are sometimes referred to as | | | | them out, the holes or pores of the purifier must be |
| pre-treatment steps, because they come before the | | | | less than 1 micron in size. The thin film composite |
| thin composite membranes used in a reverse osmosis | | | | membrane of the reverse osmosis water purification |
| water purification unit and before any disinfection is | | | | unit works to filter out the cysts, as long as it is in |
| performed. | | | | good condition. In most modern homes around the |
| The order of the steps may vary slightly, but | | | | US and the rest of the world, the thin membranes |
| typically chlorine or another chemical disinfectant will | | | | are not needed. The treatment facilities take care of |
| be added after the sediment filters have done their | | | | most particulates. It is the chemicals and other |
| jobs. A sediment filter cannot remove biological | | | | residues left behind that are most problematic. A |
| contaminants like bacteria or viruses. | | | | well-designed activated carbon system is all that is |
| Chlorine will kill most germs, but the remnants of the | | | | necessary in most homes. A sub-micron sized channel |
| chemical and the decomposing contaminants will | | | | in a hard carbon block filters out cysts. The carbon |
| remain. An activated carbon step should follow the | | | | particles trap practically everything else. In other |
| chlorination process for two reasons. First, chlorine | | | | words, you might not need a reverse osmosis water |
| and other chemicals are not filtered out by the thin | | | | purification unit in your home. Find out what you |
| film composite membrane. Second, chlorine degrades | | | | actually need, before you waste your time and |
| the membranes. Membranes exposed to chlorine | | | | money. |
| must be replaced frequently. Otherwise, they will | | | | |