Reverse Osmosis Tanks


The tank marked “A” in the foreground is the standard tank on our Black & White reverse osmosis units. “B” is the standard for our Economy RO unit.

If you're in doubt about the size tank you want, we suggest that you read our page on tank sizing.

We offer four sizes in standard undersink RO tanks. All undersink RO tanks on this page are certified under NSF/ANSI Standard 58 for Material and Structural Integrity.

There's also a 14-gallon tank at the bottom of this page. It's an undersink tank only if a small person can stand under your sink. The four tanks that will fit under almost all sinks are shown at right.

All tanks have standard stem size and can be used with 1/4" or 3/8" tank valves. All can have air added with a standard bicycle pump. All tanks have a maximum working pressure of 100 psi. All are air bladder tanks (water does not touch the metal or plastic outer shell, but rests in a butyl bladder) and all are pre-charged with air at the factory, ready to install.

We guarantee them unconditionally for one year, though a good RO tank will normally last several years. (We have some in use on local units that are over ten years old.)


Gallon Capacity & Size

Tank manufacturers are woefully inconsistent about the sizes they put on undersink RO tanks. Two tanks of identical dimensions might be called 4.0 gallons by one maker and 3.2 by another. There is no clear understanding of what the manufacturer is sizing — the outside of the tank, the maximum amount of water it will hold, or the amount of water it holds under average conditions.

Roger's RO Tank Test

To remedy this and to provide a meaningful comparison of the four undersink tanks we sell, we devised our own test of tank capacity. It was carried out (with flawless accuracy) by Roger, our main RO builder.

Roger took the four new tanks, rinsed them well, then adjusted the empty tank air pressure in each to an exact 7 psi. He then filled the tanks to exactly 40 psi with water — a likely average full tank pressure for a standard RO unit running on city water. He then emptied the tanks, caught the water, and measured the amount that came out of each tank. The chart below gives the breathtaking results.

Part #

Size & Description.

Height Is Without Tank Valve. On the metal tanks, the valve adds about 1.75" total height. The plastic tank's valve mounts on the side. (See picture.)

Approximate Capacity at 40 PSI
TA002 7.5" Diameter X 10" High. White, Metal. Compact. Comes with stand and can be side mounted. This is the standard tank on our Enhanced Performance Fluoride Filter. This is tank D in the picture above. 1.00 gal.
TA003 8.5" Diameter X 13.5" High. White, Metal. Comes with stand and can be side mounted. This is tank C in the picture above. 1.75 gal.
TA005 11.5" Diameter X 13.5" High. White, Metal. Comes with stand and can be side mounted. The is the standard tank for our Black & White and Q Series Reverse Osmosis Units. It's the standard size for most undersink RO units. This is tank A in the picture above. 2.50 gal.
TA006 8.5" Diameter X 20" High. Flowmatic Brand White, Plastic. Comes with stand and can be side mounted. This is the standard tank for our Economy RO Units. This is tank B in the picture above. 1.75 gal.

All tanks are sold without a tank valve. If you're replacing an existing tank, your old tank valve will probably work. If you want a new valve, please select 1/4" or 3/8" to match your tubing.


Standard “4 Gallon” RO Tank
Part #: TA005

  • Tank Capacity @ 40 PSI: 2.5 gal.
  • Diameter: 11.5"
  • Height: 13.5" (without valve)
Part Description Price
TA005

Standard-Sized RO Tank (The size is called 4.0 or 3.2 gallon by most manufacturers.)

$56.00 Add to Cart

This tank comes with an optional stand and it can be side mounted if desired. It stands on its bottom fine without the stand.

Tank valve is not included. To include a Tank Valve, order one of the tanks valves listed at the bottom of this page.


Flowmatic Plastic Tank
Part #: TA006

  • Tank Capacity @ 40 PSI: 1.75 gal.
  • Diameter: 8.5"
  • Height: : 20" (without valve)
Part Description Price
TA006 Flowmatic Plastic RO Tank. $63.00 Add to Cart

This tank can side mounted if necessary. This is a very heavy duty plastic tank that won't dent or rust. Fits into very tight spaces.

Tank valve is not included. To include a Tank Valve, order one of the tanks valves listed at the bottom of this page.


Petit White Metal Tank
Part #: TA002

  • Tank Capacity @ 40 PSI: 1.00 gal.
  • Diameter: 7.5"
  • Height: : 10" (without valve)
Part Description Price
TA002 White metal petit RO tank. Comes with optional stand and can be side mounted. $43.00 Add to Cart

Tank valve is not included. To include a Tank Valve, order one of the tanks valves listed at the bottom of this page.


Mid-Sized White Metal Tank
Part # : TA003

Tank Capacity @ 40 PSI: 1.75 gal.
Diameter: 8.5"
Height: : 13.5" (without valve)

Part Description Price
TA003 Compact White Metal RO Tank. $49.00 Add to Cart

This is a very versatile tank that fits into tight spaces. Note that the capacity is the same as TA006.

Tank valve is not included. To include a Tank Valve, order one of the tanks valves listed at the bottom of this page.


Flowmatic Metal "14 Gallon,"  Really Big RO Tank
Part # : TA008

  • Tank Capacity: “14 gallon” (Manufacturer's size. We haven't tested it.)
  • Diameter: 15"
  • Height: 23"
  • ROPRO (Flowmatic) 14 Gallon Reverse Osmosis Tank. The tank accepts any standard RO tank valve, including the John Guest valves shown on this page. This tank must stand upright.

    Part Description Price
    TA008 ROPRO metal reverse osmosis tank. $159.00 Add to Cart

    Tank valve is not included. To include either a 1/4" or a 3/8" tank John Guest Tank Valve, add it to your order. Either the 1/4" or the 3/8" valve will fit the tank.



Tank Valves Ordering Chart

Part Description Price
JG014 1/4" John Guest Tank Valve (fits all tanks above) $7.00 Add to Cart
JG015 3/8" John Guest Tank Valve (fits all tanks above) $7.00 Add to Cart

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