I would like to know how good under sink water purifiers work.the water in my area is not that bad but it seems like it has a lot of calcium type deposits in it.
I notice a white deposit around my tea pot.
Thanks
mikeyg...

Mikeyg,
I am going to discuss technologies instead of particular brands.

Sediment filtration- is not necessary on municipal water supplies. Typically, these filters are spun poly-composite materials, pleated filters, or believe it or not wrapped string.

Granular Carbon- it helps to remove taste and odor contaminants such as chlorine, chloramines, sulfur, manganese, etc. But because it is loose grains of carbon in a cartridge, it is not effective at all in removing small particulates. It is okay as a pre or post filter in a micro-filtration arrangement.

Carbon Block- Imagine forcing the water through a dense brick. That is what pressing water through a carbon block filter is like. They compress carbon together into a block. This causes more contaminants to be removed. In addition, it will remove many gaseous, and oil based contaminants. A good carbon block filter will remove items such as MTBE, pesticides, volatile organics (voc), lead, etc, However, it will not remove beneficial trace minerals, and fluoride that your municipality injects for strong teeth.

Reverse Osmosis- Imagine pressing water through plastic wrap. That is literally what an RO membrane looks like. It has tiny perforations, and with many wraps the perforations don't line up. They push the water through so slowly because of the force it takes. That is why they have a storage tank. So it really produces 99% mineral free water. There are times where RO is best, however in my opinion a good quality carbon-block will produce safe water without stripping it of all minerals. Our bodies need minerals. RO water is very sterile tasting to me. That is why bottled water companies put minerals back into the water when they use RO filtration. Another disadvantage to RO is that it is wasteful. An average RO wastes as much water as it makes. In other words... to make 1-gallon of finished water, it wastes 1 gallon. One other disadvantage to RO is the amount of room that it takes under the sink. An RO will take up half of your under-sink area. Generally, you should have a water softener treating your water if you are going to have an RO. This is because the microscopic pores in the membrane will clog up with calcium deposits without a softener. Generally a RO has 4-6 stages, which means that there are 3-5 filters to change once a year, and the membrane once every 2-3 years. There are certain times that it is required such as nitrate removal, sodium removal, etc. But on a municipal supply, they have to treat for those contaminants already.

Ultra-violet- Although your municipality treats for bacteria, they don't test everyday. Bacteria makes you sick fast. E-coli, fecal, crypto-sporidium, influenza, etc. can all thrive in water. I have been through many water safety/ security courses every since 9/11. They have been concerned about terrorists attacking with biological (bacteriological) weapons in our water supplies. A UV system helps to ensure safety by killing biological growths at your point of use.

My preference is a top quality carbon block, along with UV. It won't remove as much calcium as an RO though. If you really want that scale removed, you'll have to use RO, or have a softener to treat your house.

Hope that helps.
Al

I totally agree with albinfla regarding the list of filters, its complete. The RO system is a bit tricky to install compared to the others but many home owners could do it, about $300.