Background
Our water has gunk in it (possibly due to this construction). This gunk gets caught in our kitchen faucet’s aerator, and if we don’t clean it out, the water flow will stop completely. Here is what the gunk looks like:
So we decided it was time to install a water filter. The easiest way to filter drinking water is to use a Britta and Pur pitcher, but these don’t work for me. I use them for a bit, and then get tired of changing the expensive replacement filters every month.
The water filter industry has a standard size for under-sink adsorption filters: 9 3/4″. These filters are similar to but much larger than the standard Britta pitcher-style filter, and they only need to be changed every 4-12 months (depending on filter type). You can buy 9 3/4″ filters from several different manufacturers, which helps keep the prices down.
Choosing a Filter
Deciding what kind of filter you need should be easy. In theory, you can call your water utility (or check their website), find out what contaminants are in your water, and then check which filters are certified by the NSF to filter out those contaminants.
I did a bunch of research and found that SF tap water is generally safe to drink. It is disinfected with Chloramine and contains trace amounts of parasites, copper, and lead. The SF PUC monitors Cryptosporidium and Giardia levels every two weeks, and their 2006 Water Quality Report (published 6/07 PDF) shows that all measurable contaminants are below maximum contaminant levels.
Even after finding that SF water is safe for us to drink, I decided to get an activated carbon filter in addition to a sediment filter, because I’m worried that chemicals might enter into the water main during construction, just as visible sediment enters into the water main. Also, I decided that activated carbon was really cool (one gram has a surface area of 500 m² - 1500 m²)!
Choosing a 9 3/4″ Filter Housing
My first thought was to get an OmniFilter OT32 for $140. This unit has a double housing that can fit 2 9 3/4″ filters, and it comes with a string-wound sediment filter and an NSF-certified 0.5-micron enhanced carbon block filter.
After some digging, I found I get a cheaper 2-filter housing from Pentek Filtration. I bought a BFS-201 housing (PDF) from FiltersFast for $57. It’s seems well-built and looks like this:
Installing the Filter Housing
The recommended way of using under-sink filters is to install a second, low-flow-rate faucet to get the maximum effect from your filter. I didn’t want to do this, because I didn’t want to drill a new hole through our granite countertop, so I investigated splicing the filter into our cold water line.
If we only wanted to filter sediment, we could easily add the filter to cold water line, because sediment filters can handle 10 gallons per minute, and our faucet only had a 2gpm flow rate.
Unfortunately, activated carbon filters only work at reduced flow rates. If you only want to filter for what the NSF calls “Aesthetic Effects” (Standard 42), then you can buy a carbon filter that works at 2gpm. But if you want to filter for things like lead, mercury, VOCs, asbestos, MTBEs, Cryptosporidium, and Giardia (what the NSF calls “Health Effects”, or Standard 53), then you have to reduce to the flow rate to 0.5-0.6 gpm.
We decided that it was OK to reduce the flow rate of the cold water at the faucet, since we will still have the full hot water flow rate for washing, and the dishwasher cold supply is already split off. This means we don’t need to drill for a new faucet.
The Pentek filter housing has two 3/8″ female NPT water connections. Our cold water line has a 1/2″ IP straight thread on the faucet side and a 3/8″ compression fitting on the other. To splice the housing into the cold water line, we need to add two 3/8″ NPT to 3/8″ compression adapters to the filter housing, using teflon tape to ensure a good seal:
Choosing a Sediment Filter
Now comes the fun part! We get to choose some filters. Since these are a standard size, we can choose from a bunch of brands, and mix-and-match. Sediment filters are very inexpensive. They are usually made of wound string, last for 10-15,000 gallons, and cost under five bucks. I got the Pentek CW-MF from FiltersFast for $3.30. Looking at the spec sheet, I should have gotten the WP-5 for $5.60, since it has a 5 micron rating instead of a 30 micron rating. It might not matter, since the water will be flowing through a carbon filter anyway. This filter is mostly to lengthen the life of the carbon filter.
Choosing an Activated Carbon Filter
The OmniFilter CB3 seems pretty good. It costs $36 dollars and has NSF Standard 42 and Standard 53 ratings to reduce Asbestos, Atrazine, Cyst, Lead, Lindane, Mercury, and VOCs, as well as Chloramine and Chlorine.
I found Pentek CBR2-10R, which is basically the same thing as the OmniFilter CB3, but it lacks the NSF Standard 53 rating. However, it costs only $17 at FiltersFast, and I decided it was good enough for me. It also has a built-in 0.6gpm flow restrictor, which makes sure you get the full effect of the filter.
After installing everything, this is how it looks:
The water definitely tastes different; it has a slightly-metallic aftertaste, similar to distilled water. I’m interested to see how much stuff the sediment filter catches after 3 months.
Costs
This is my bill from FiltersFast:
Filter Housing BFS0-201 $56.99
Carbon Filter CBR2-10R $16.95
Sediment Filter CW-MF $3.30
Filter wrench SW-1a $2.70
Shipping $1.99
retailmenot.com coupon -$5.00
Total $76.93
I also had to buy two 3/8″ compression to 3/8″ MPT adapaters for $4.79 and a couple hoses from Cole Hardware, bringing the total up to a hundred bucks.
I was inspired by peliom’s web-2.0 Japanese flashcards, so I made some Hindi flashcards this weekend. Or rather, I made an open-source framework for javascript-powered flashcards called 
