ASK, WHY REVERSE OSMOSIS? -- Bottled water is ubiquitous; people realize the need to keep hydrated with clean water. Clean water tastes better and makes coffee, mixed beverages, tea taste better. It's also safer for baby formula and pets. But bottled water is expensive, you don't really know where it came from, and puts tons of plastic into our landfills. A reverse osmosis system can provide almost 100% pure water at home for pennies per gallon. Repeatedly fill your water bottle from your own source!
DECIDE ON A SYSTEM TYPE -- When I bought my reverse osmosis systems, I did some searching on the internet first. There are basically two membrane types: CTA (cellulose triacetate) and TFC (thin film composite). CTA is chlorine resistant. TFC is more efficient than CTA; however, TFC membranes are sensitive to chlorine, so if you have chlorinated source water, you must buy a system with a carbon prefilter to remove the chlorine. So with well water, I used a TFC system. With our current municipal water, I have another TFC system with a carbon prefilter.
CHOOSE A SYSTEM CONFIGURATION -- Most people will want a system that goes under the sink, with a faucet to dispense the water. This configuration is pretty standard and looks like the picture here, with the 3 long filter canisters and membrane, a pressurized holding tank, and a faucet. In fact, this is the same system I have now. If your only need for pure water is for aquarium or gardening (orchid) use, then a system without the tank and faucet is appropriate, and cheaper. These are also more portable and can be connected to a garden hose.
One last thing -- if 95-98% pure water is not enough for you, you can remove the last bit of impurities with an additional deionizing (DI) filter to get 100% pure H2O.
FIND A SYSTEM -- By far, the cheapest place to buy a reverse osmosis system is online. For less than $200, you can get a good system that will last a lifetime with regular maintenance. Personally, I look for someone who builds their own systems and has been in the business for while. They will not be pushing a particular brand, can find quality parts for the system, will help you personally with questions, and sell replacement filters at quantity discounts. Check on eBay. But if you like name brands and company-oriented service, then by all means buy from an online retailer... you will probably just pay a higher price for more peace of mind.
A couple things you may want to buy along with your system. 1) A TDS meter to measure the total dissolved solids in your output water. This will help you know when to change the filters. 2) A refrigerator kit to connect the system to your fridge for cold, clean water and crystal clear ice.
INSTALL YOUR SYSTEM -- Of course, each system and situation is different, but I can give you some general guidelines. Installation is easy for someone who is handy with a drill and with some basic plumbing experience. If you have doubt, you can always hire a plumber or a handy friend to help install it for you.
1) Try to fit the system under the sink. If not there, then in an adjacent cabinet or below the floor in the basement. You want it as close to the water source and sink as possible.
2) Connect the output tube from the system to the sink waste pipe.
3) Connect the source water tube to a cold water pipe using either a saddle valve (sometimes included in the kit) or by inserting a "T" into the cold water pipe for the sink. Remember to put a shutoff valve on this connection.
4) Install faucet -- I used an existing hole in the sink that was for the sprayer, and bought a combo sink faucet/sprayer to replace the original.
5) Install refrigerator line. I drilled a 1/4" hole through the bottom of the cabinet and floor and ran the tube down, over and up through another 1/4" hole in back of the fridge. This line connects with a "T" into the line that runs up to the faucet.
CYCLE THE SYSTEM -- Turn on the feed water and let the holding tank fill. Empty the first 1 or 2 tanks of water... just to flush out anything that was in the filter canisters and the carbon dust. Then you're in business! My reverse osmosis water is consistently around the 4-8 TDS range. When it starts getting above 20 or so, I know it's time to change the filters.