Pure Water Occasional

Special Mid-Month Issue

April 15, 2012

Read This Issue on The Pure Water Occasional Website

Installing Undersink Water Treatment Units In Tight Places


In the last decade, installing undersink water treatment devices has gotten a lot easier. The advent of quick-connect fittings has played a big role, as has also the widespread use of flexible sink faucet connectors and tube-attached ledge faucets.

On the other hand, some new challenges have surfaced. These include granite countertops, which require special tools and skills to make a faucet hole, and especially the shrinking of undersink space. For reasons unknown, as homes get larger and more elaborate, and as undersink appliances like disposals get larger, space under kitchen sinks gets smaller.

Here is some information about installing filters and reverse osmosis units in tight spaces.

Installing in Tight Places

One of the most frequently asked questions that we get from undersink reverse osmosis and filter purchasers is, "Will It fit under my sink?" To help answer this question, here are some size charts for our standard undersink filters and reverse osmosis units.


Undersink Filters. Most Popular Sizes
Model Height Width Depth Comment
Black and White Double Filter 14" 10" 5.5" Can Wall Mount or Lie on Its Back
Black and White Triple Filter 14" 16" 6" Can Wall Mount or Lie on Its Back
Q Series Double Filter 15.5" 6" 3.5" Can Wall Mount or Lie on Its Back
Q Series Triple Filter 15.5" 9.5" 3.5" Can Wall Mount or Lie on Its Back


Reverse osmosis units are a more complicated issue because they have a storage tank. Finding room for the unit means finding a place to hang or stand the main unit, plus a place for the storage tank to stand. The tank, fortunately, doesn't have to be next to the unit. It can be situated anywhere a single tube can connect it to the main unit.

RO storage tanks now come in many sizes, and this makes things easier, because it's surprising how many places you can squeeze in an 8" diameter tank where an 11" diameter tank won't fit.

The following table gives tank capacities and exterior dimensions. Most tanks can lie on their sides if necessary (see pictures below). For more information about the meaning of "capacity" figures, see the tank page on our main website. The tanks pictured there are those described in the following chart.

RO Tank Dimensions
Description Height Diameter Comment
2.5 Gallon Metal Tank. (Standard tank for all of our RO units.) 13.5" 11.5" Tank Valve adds about 1.75" to height.
1.75 Gallon Metal Tank. 13.5" 8.5" Tank Valve adds about 1.75" to height.
1.75 Gallon Plastic Tank 20" 8.5" Tank Valve mounts near the bottom on the side. Does not add to height.
1 Gallon Metal Tank. 10" 7.5" Tank Valve adds about 1.75" to height.


Here are dimensions of our standard-sized RO units. These can wall mount or lie on their backs.

Full-Sized Reverse Osmosis Dimensions
Unit Description Height Width Depth
Black and White 3 Stage 18" 14.5" 5.5"
Black and White 4 Stage 18 15 6"
Q Series 3 Stage 19" 13.5" 5.5"
Q Series 4 Stage 19" 14.5" 5.75"



Doug's RV

Local Installation

A tight RO installation behind the sink of a Recreational Vehicle. The Pure Water Products "Gold Series" unit, made with inline filters and standard-sized membrane housing, will fit into a large shoebox. The permeate pump (floor mounted behind the RO unit) saves water and provides maximum performance with minimum water pressure. The pump, the storage tank, and the RO unit are all secured to the floor with screws to keep them in place on bumpy roads. The faucet is mounted on the sink on the other side of the wall.

The Gold Series unit isn't on our website, but if you want one, please call. Installation and photo by Roger. Larger Image.


Here is another tiny RO unit. This one can be mounted directly to the wall.

Gold Series
The unit above was built on a board to illustrate how compactly a reverse osmosis unit can be installed. The unit needs uses no bracket. The two filters and the membrane housing are mounted on clips. With this design, an RO unit can be worked into almost any tight area. The parts do not even have to be mounted on the same wall. It extends out from the wall less than 4" at its widest point. Photo by Joe.

Space Saving Tips

1. When you install, remember that you're going to have to perform maintenance service on the unit eventually. If you have a choice, hang the main unit on a wall at the front of the cabinet. RO tanks can be placed in back. (See the picture below.)

2. If the storage tank is too large to be pushed to the back of the sink cavity, you can often get it there by uninstalling a drain pipe. Drain pipes are usually easy to remove and to put back in place.To service the storage tank, you need only to be able to reach it with your air pump hose.

3.The faucet is usually the most difficult-to-reach part of the installation, so install it first so you won't have to work around other parts of the RO unit.

4. If space is tight, a tube-attached faucet is much easier to install than a conventional faucet. This is not not just because you don't have to install the tube, but more importantly because you can actually run the small parts like the washers and the lock nut up the tube. If you drop a part, you don't have too look for it because it stays on the tube.

5. If there is no way to drill a hole in the sink--and with modern sinks, sometimes there isn't--filters and even reverse osmosis units can be installed so that the treated water comes out of the cold water faucet on the sink. This is not an ideal arrangement, but it works fairly well with filters. It should be a last resort with RO units, because of low water availability and, frequently, incompatibility of low-TDS RO water with sink faucet metals. See a discussion of "simple" vs. standard units in the Occasional's "How It Works" section.

6. Storage tanks can, if necessary, be installed in a cabinet adjacent to the undersink cavity. By drilling a small hole through the cabinet wall, a tube can be run to connect the tank to the main RO unit.

Christie's RO
A Q Series RO unit installed in a tight spot. We were able to work the storage tank behind the drain pipe by placing it on its side. Note that the blue-capped air port is turned outward to make the tank easy to access at service time. (Photo and installation by Adrienne.)


And, Finally, A Common-Sense Reminder From Pure Water Annie

Annie Small
Just as flowers need water and sunshine, water filters need cleanliness and order

This seems so obvious that I'm reluctant to say it, but the best way to create undersink space is to get rid of things you don't need. Undersink clutter not only makes installation difficult. It is often the cause of leaks and malfunctions as well.

Installing an undersink water treatment system should be a liberating experience. In many cases the homeowner is freeing himself from the drudgery of lugging and storing water bottles. Why not view it as an opportunity to free yourself at the same time of the many unnecessary bottles, brushes and bags that accumulate as if by magic under kitchen sinks? How many half-used boxes of Bippy Cleaner do you really need?

Undersink clutter causes leaks and it frequently hides tiny leaks until they cause real water damage.

When you empty your undersink to install your water filter, be very selective about what you put back.


Cluttered RO
Tight spaces are often created by attempting to store 50 or more mostly empty bottles of household chemicals in an otherwise adequate undersink space. Bottles were completely hiding the storage tank and most of the RO unit before they were removed to allow us to service the unit. Photo by Adrienne.



The Pure Water Occasional is a project of Pure Water Products. Please visit our websites:

Main Website: www.purewaterproducts.com. This site features our full range of products, plus instructions, technical articles, product manuals, and more.

The Occasional's Website: www.purewateroccasional.net. In addition to archiving back issues of the email Occasional, this site houses a sizeable section about water contaminants, a "how things work," series, a new products section, a glossary of water treatment terms, and, "much, much more."

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