How to Install an Undersink Reverse Osmosis Water Filter

Although the water quality in the United States is generally good, it varies from city to city and the water treatment effectiveness varies from day to day. Chlorine used to kill pathogens can produce worrisome byproducts like chloroform and possibly damage copper and PEX piping system. (See articles http://knoji.com/causes-and-solutions-for-copper-pinhole-leaks-in-residential-plumbing-systems/ and http://knoji.com/problems-with-pex-fittings-the-class-action-lawsuits/ ) The water quality of millions of private wells is also a concern since there are no requirements to test them after installation. This is why there has been a surge in the installation of filters for drinking and cooking water.

Although there are numerous products and solutions to treat water quality issues, no one system can correct every problem unless you have a professionally installed system costing thousands of dollars. To start with you should send a sample to a state-certified lab for testing. Your state health department or county extension office will be able to recommend an independent lab. Basic tests, for bacteria, nitrates, heavy metals and the most common pesticides, run $30 to $50. Usually the more items tested for will increase the cost of the tests.

If tests reveal no unhealthy pathogens, metals or compounds in excess of Environmental Protection Agency (EPA) limits, there's really no compelling need for treatment. If you don’t require treatment do install a filter system, some are expensive to buy and use and all require periodic maintenance.

Water Quality Overview

If tests reveal a water-purity problem, you should contact a professional treatment company or your state health department since one water condition often can hinder treatment of another. The membrane in a reverse-osmosis (RO) unit, for example, is easily clogged by hard water, so you may need to install a softener before you can filter for nitrates or heavy metals. Reverse osmosis units can't handle bacteria, so some rural situations or homeowners with well water may require chlorination equipment.

In general, sand, rust and suspended iron and manganese are treated with a sediment filter. A rotten-egg smell, from hydrogen sulfide, is best treated with chlorination and a sediment filter. Residual chlorine and other odor and taste problems can be treated with an inexpensive carbon filter. Carbon filters also do a good job on volatile organic compounds, radon and certain pesticides.

You need to use a softener on hard water and a neutralizing filter on acidic water. Heavy metals, including lead, mercury, arsenic and cadmium, plus sulfates and nitrates, are best treated with a reverse-osmosis unit. Countertop distilling equipment can handle bacteria, heavy metals and organic compounds, but they need frequent cleaning and use plenty of electricity and are prone to scale build-up.

See my article about water softeners at: http://knoji.com/the-facts-about-water-softeners/ .

Installation

Reverse-osmosis kits are typically installed next to your kitchen sink and treat only drinking and cooking water. The treated water is delivered through a dedicated spigot. They work slowly, so they need to be sized to meet the household's specific needs, 3 to 5 gal. per day works well for households with 4 or 5 people. An RO unit usually consists of several filters working in series, and there are several configurations and sizes to choose from.

Most units range in price from $150 to $300. A typical kit might include a 5-micron pre-filter, a reverse-osmosis membrane and a granulated activated-carbon post-filter, plus a 3 to 5 gallon storage tank and a faucet equipped with backflow preventer. They are sometimes called 4 or 5-stage RO systems depending on how many filtering stages there are. Most kits will have color-coded plastic tubing and saddle valves for the water supply and wastewater saddle tap which goes to the PVC drain just below the sink.

RO units utilize a semi-permeable reverse-osmosis membrane, which comes in the form of a replaceable cartridge. Water pressure from your domestic water lines forces water molecules through the membrane, but you typically need at least 60 psi for the RO system to work. The membrane is very dense which prevents foreign matter from going through it. This water is sent to the storage tank under the sink, while the wastewater is flushed into the sink drain. The wastewater will have a higher level of contaminants than the original water.

The pre-filter placed before the RO membrane strains out dirt and sediment. A granulated-carbon filter after the RO membrane removes any bad flavor and some contaminants that the membrane can't handle.

Reverse osmosis is a slow, inefficient process that wastes 40 percent of the water brought to the membrane, but it is very effective in removing some of the worst contaminants.

Installation Steps

Installation varies by manufacturer but these steps will give you a good idea of what is involved.

Most RO membrane cartridges are inside a sealed plastic bag containing a packaging liquid used to prevent bacteria growth. You should wear clean gloves or wash your hands thoroughly before handling the cartridge to prevent contamination. Touching only the ends, insert the cartridge into the filter housing and install the cap.

The units are designed to be installed inside your kitchen sink cabinet, but you can install them in another location provided you can obtain longer tubing for the connections. Once the RO membrane is installed, mark a cabinet wall through the filter bracket and install the bracket screws. Since most kitchens have dishwashers, the opposite side of the cabinet works better than the rear of the cabinet. Hang the filter assembly on the bracket.

Wrap Teflon tape around the male threads on the storage tank fitting and thread the valve into the tank. Tighten the valve about one turn past finger-tight. Set the tank in an unused corner of the cabinet and connect the tube from the membrane outlet. Most manufacturers now use nylon compression fittings, so be careful not to over-tighten them.

To install the faucet, remove the cover from the sink or bore a new hole for the faucet if your sink comes equipped with a faucet sprayer. Stainless steel and solid surface sinks are easy to cut through, but if your sink is cast iron or enameled steel, you'll need to bore the counter next to the sink. Check with the installation instructions for the proper size for your unit, usually they are 1 to 1 ¼ inches in diameter.

Insert the faucet in the hole and slide the spacer onto the shank from below and tighten the locking nut. The tubing is usually connected to the bottom of the faucet by way of a push-fit connector. It will bottom out when it is properly seated.

Most units come with two additional nipples, both push-fit barb fittings for the water supply and wastewater hook-up.

You need o tap into household water line with a saddle valve included in most kits. Clamp the saddle securely around the cold-water supply and tighten the fastening bolt Connect the supply tube to the saddle tap and tighten until it feels snug. Thread the tap spike into the riser when you test the system.

To drain the wastewater you will need to drill a 5/16-in. hole in the sink drain opposite the disposer or dishwasher drain. Install the drain saddle over the newly made hole and tighten the saddle bolts. Then install the drain tube in the saddle and tighten the compression fitting.

Startup Procedures

RO kits are vulnerable to microbiological contamination, so they're shipped with a preservative solution inside that produces flu-like symptoms if ingested. The carbon filters contain carbon dust that need to be flushed away.

Be sure you flush two tanks of water, about 5 gallons, through the faucet before consuming any of the water. This may take as long as two days, depending on supply water pressure and condition.

Wastewater Usage

If you are concerned with the water use associated with RO systems, consider the fact that you are primarily using it for drinking and possibly cooking. A family of four may drink 2 gallons of water a day and add another 2 gallons for cooking. This would mean that for every 4 gallons of filtered water, you would have 3 to 4 gallons of wastewater.

You can come up with some creative ways to use this water; after the initial flushing of the system and membrane. The best way I have seen is to run the drain line to a 5-gallon bucket in your basement and use this water to water you indoor plants or garden. If you have a rain barrel, you can dump this water into that as well. You can use the water to mop floors, clean windows, or dump it in your washing machine while it is filling up; the water supply shuts off when the level reaches a certain level so pour it in slowly. You can also use it to flush a toilet or two if you are that adventurous.

Maintenance Concerns

Most units require that the filters be changed every 6 months and the RO membrane every two years. You should consider this cost when considering which system to install.