With every passing year we learn more about what is in our water and the effects those contaminants can have on our health. It takes the EPA years of study to figure out what is an acceptable level for contaminants in our water or how best to treat them. Contaminants in residential drinking water can include almost anything, from industrial waste that was dumped in a river, to fertilizers and household cleaning products. Many times, treatment involves adding a chemical to the water to neutralize the contaminant—for instance, chlorine is added to water to control the amount of microbes—but these chemicals can give water undesirable tastes or odors. Technology like reverse osmosis systems exists to remove contaminants from water without adding any chemicals.
Reverse osmosis (RO) systems are becoming an increasingly important, needed appliance in our homes. RO systems utilize your water pressure and a semi-permeable membrane to reduce contaminants for great-tasting water without adding any chemicals. They are typically used to purify drinking water which is where contaminant levels matter the most. Some areas, however, have such terrible water that an RO system is used for the entire home.
Every reverse osmosis system has at least four parts: a prefilter, an RO membrane, a storage tank and a postfilter. Water supplied by the city or a well enters the system through the prefilter, which protects and extends the life of membrane by filtering out the things that can harm it, like chlorine and sediment.
A reverse osmosis membrane uses a semi-permeable membrane to separate water molecules from other molecules. “Semi-permeable” means that some things can pass through and others can’t. A familiar example would be your furnace’s air filter, although, semi-permeable membranes for water treatment allow passage based on the size of the particle as well its molecular charge whereas typical air filters separate the contaminants exclusively by size. Holes or pores in the membrane are sized just big enough for the passage of a water molecule—even small contaminants such as tobacco smoke or paint pigments are too big to go through an RO membrane. At this point, because the membrane only lets certain molecules pass through, there is some waste liquid with a highly concentrated amount of contaminants that goes to the drain. The virtually contaminant-free water that makes it through the membrane, called a permeate stream, is safe to drink and tastes great.
Reverse osmosis technology relies on pressure to push the water molecules through the. Water pressure varies with your water source. City water is usually supplied between 40 and 100 psi (pounds per square inch). Well water is usually less pressure, delivered between 20 and 60 psi depending on your pump. The production rate of the membrane is dependent on factors such as temperature, pressure and Total Dissolved Solids levels. Because flow and production rates vary, most RO systems also have a storage tank, allowing more pure drinking water to be available on demand, so you can fill your glass or pitcher much faster.
Because the water is so pure, bad tastes and odors from the storage tank’s bladder and walls can find their way into the water during prolonged contact, so they must be taken out. That’s why a postfilter is an important part of the reverse osmosis system; any odors or tastes picked up from the storage tank are removed and the water is once again great-tasting.
To raise the pH if it is too low, whole house systems use a “polisher” after the postfilter, which adds minerals to the water which protect the pipes and which come people feel enhances the water’s taste.
Sometimes seeing is believing. Personally, I love seeing ice cubes made with RO water because they are virtually colorless. Ice cubes made from city-supplied tap water are almost white in color, which tells me that there are minerals mixed in with the water molecules. Whenever I see transparent ice cubes, I know the RO system must be removing a lot from my water. If your home has questionable drinking water, maybe it’s time to check out a reverse osmosis drinking water system—you won’t regret it.
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