Around the world, household drinking water purification systems, including a RO step, are commonly used for improving water for drinking and cooking.
Such systems typically include these steps:
* a sediment filter to trap particles, including rust and calcium carbonate
* a second sediment filter with smaller pores
* an activated carbon filter to trap organic chemicals and chlorine, which degrades certain types of thin-film composite membrane
* an RO thin-film composite membrane
* an ultraviolet lamp for sterilizing any microbes that survive RO
* a second carbon filter to capture chemicals that survive RO
In some systems, the carbon prefilter is replaced by a cellulose triacetate (CTA) membrane. CTA is a paper by-product membrane bonded to a synthetic layer that allows contact with chlorine in the water. These require a small amount of chlorine in the water source to prevent bacteria from forming on it. The typical rejection rate for CTA membranes is 85–95%.
The cellulose triacetate membrane rots unless protected by chlorinated water, while the thin-film composite membrane breaks down in the presence of chlorine. The thin-film composite (TFC) membrane is made of synthetic material, and requires the chlorine to be removed before the water enters the membrane. To protect the TFC membrane elements from chlorine damage, carbon filters are used as pre-treatment. TFC membranes have a higher rejection rate of 95–98% and a longer life than CTA membranes.
Portable RO water processors are sold for personal water available. To work effectively, the water feeding to these units should be under pressure (typically 280 kPa (40 psi) or greater). These processors can be used in areas lacking clean water.
US mineral water production uses RO. In Europe such processing of natural mineral water (as defined by a European directive) is not allowed. In practice, a fraction of the living bacteria pass through RO through membrane imperfections or bypass the membrane entirely through leaks in seals.
For household purification absent the need to remove dissolved minerals (soften the water), the alternative to RO is an activated carbon filter with a microfiltration membrane.