Well Water Pressure Tanks

Fiberglass vs Steel Well Pressure Tanks: When a WellMate Beats a Well-X-Trol, and When It Does Not

I have installed pressure tanks for 32 years, and we have sold both kinds. An earlier version of this page told you fiberglass was the tank for acidic, iron or sulfur water. It was wrong, and this is the corrected version: what a fiberglass tank actually is, the one situation where it is the better tank, what the spec sheets say, and why I still put a steel Well-X-Trol in almost every house.

What a fiberglass pressure tank actually is

A fiberglass pressure tank is a plastic tank with a fiberglass jacket: a polyethylene liner holds the water, fiberglass strands set in epoxy give it strength, and a polymer air cell hangs inside. There is no steel anywhere in it, which is the whole selling point: nothing to rust, nothing to dent, no paint to scratch.

Every pressure tank works the same way: air on one side of a flexible barrier, water on the other. In a WellMate the air is inside the bag (the air cell) and the water surrounds it. In a Well-X-Trol the water sits in the bottom under a butyl diaphragm and the air is on top. Either way the water is in a plastic chamber. The only metal on the wet side of a Well-X-Trol is the connection at the bottom, and on the current Pro Series that is stainless steel.

That last detail is the one that matters for the rest of this article. Fiberglass earned its reputation against old steel tanks with a plain steel or iron connection at the bottom. Those did rust, from the wet side, especially on acidic water, and they leaked onto basement floors. Amtrol fixed that by going to stainless. The reason to buy fiberglass in 2026 is not what the water does to the inside of a tank. It is what the room does to the outside.

Do you need fiberglass for acidic, iron or sulfur water? No.

Acidic water, iron and sulfur do not shorten the life of a steel Well-X-Trol, because the water never touches the steel. If your water is aggressive, the fix is treatment installed after the tank (an acid neutralizer for low pH, an iron filter for iron and sulfur), not a different tank. I want to be blunt about this because the wrong version was on my own website.

In July a caller from Michigan wanted a WellMate for a garden well with high sulfur, because our own site had told him to. I told him what I am telling you: sulfur is not going to affect a Well-X-Trol. Get the 203. What acidic water eats is the brass tee, the copper lines, the pressure switch fitting, your faucets and the inside of your water heater. You protect those with a neutralizer downstream, not with a plastic tank upstream.

How common is truly acidic water? Across the 325 certified lab reports our customers have run through us that include a pH result, the median is 7.6. Twenty-five of them (8 percent) came back under pH 6.5, and 12 (4 percent) under 6.0. Those homes need an acid neutralizer. Their pressure tank choice is the same as everyone else's.

The one part acidic water used to attack is the bottom connection on older tanks, and on the cheaper tanks that still use an iron elbow. The Pro Series connection is stainless, which is why we sell only the Pro Series and why the old horror stories do not apply to the tank you would buy today. If your old steel tank rusted at the bottom fitting, you do not need to switch materials; you need the current tank. Our best well pressure tank guide goes through the Pro Series part by part.

Where fiberglass wins: when the outside of the tank gets wet

Fiberglass is the right tank when a steel tank would rust from the outside in: an unheated well house with a dirt floor, a crawl space that stays damp, a pump shed near salt water, or a spot where the last two steel tanks came out with rust streaks and a puddle underneath. A steel shell sweats in humid air because the water inside it is cold, and a shell that stays wet on the outside for years will eventually rust through its finish. A fiberglass shell has nothing to rust and does not sweat the way steel does. That is a real advantage and I am not going to pretend otherwise.

The second real advantage is weight. The chart below is straight from the manufacturers' spec sheets: at the 32-to-40-gallon size a WellMate WM-12 is 35 pounds and a FlexLite FL-12 is 33.5 pounds against 47 for the Well-X-Trol WX-203. At the 44-to-47-gallon size it is 46 and 47 pounds against 65. If you are carrying a tank down a ladder into a pit or across a yard to a well house by yourself, 12 to 19 pounds matters. In a basement with stairs, a 47-pound tank is a one-person job either way, and this advantage mostly disappears.

You will read that fiberglass is 40 to 60 percent lighter than steel, or that a steel tank this size weighs 90 to 120 pounds. It does not. Amtrol's submittal sheet puts the WX-203 at 47 pounds shipping weight. The old figures come from comparing a small fiberglass tank against a big commercial steel one, or from the days before deep-drawn steel shells. Use the real numbers.

I have also had one caller tell me the fiberglass tank on his old farm well gave the water a taste, and that his Well-X-Trol never did. I cannot verify that and I would not choose a tank on it. Pentair certifies the WellMate to NSF/ANSI 61 for drinking water contact, the same standard as everyone else. I mention it only because you may hear it too.

Where steel wins: pressure, warranty, temperature, and the fine print

On every number the manufacturers publish, the steel Well-X-Trol is the stronger tank: 150 psig working pressure against 125 for WellMate and FlexLite, a 7-year warranty against 5, and a 200°F operating limit against 100°F internal for the WellMate and 120°F for the FlexLite. None of those numbers matter on a normal day. A 40/60 system tops out at 60 psi and well water comes in cold. They matter because a manufacturer sets its warranty and ratings based on how the tank behaves in the field, and Amtrol is willing to stand behind its tank two years longer at 20 percent more pressure.

The fine print is where fiberglass gives back some of what it gained on weight. Pentair's WellMate catalog requires flexible connectors between hard piping and the tank, and a vacuum breaker on any system that can pull suction on the tank (a draining line on a hillside can); skip either one and the warranty may be void. It also sets a 40°F minimum and 100°F maximum water temperature. A steel tank has none of those conditions. Well contractors who post fiberglass tank failures online show two things: leaks at the top seam or air cell, and shells that went soft after years in a sun-lit shed. Pentair sells a UV-protected version of the tank for outdoor use, which tells you the sun is a factor the manufacturer takes seriously. In a basement neither problem comes up, but a basement is also where fiberglass has no advantage to begin with.

The 7-year warranty is not an abstraction. If a Well-X-Trol fails inside seven years, you carry it to any plumbing supply house that stocks Amtrol and walk out with a new one; if a plumber installs it you pay labor only. I have seen brand new tanks go up in four years, usually a defective diaphragm, and I have seen Well-X-Trols we replaced that had run 30 to 40 years. The warranty is the manufacturer telling you which end of that range it expects.

Four minutes on why the Well-X-Trol Pro Series is the tank I recommend, how a pressure tank works, and how to tell when one has failed.

The replaceable air cell: a real feature almost nobody uses

The WellMate's air cell can be replaced in the field, and the Well-X-Trol's diaphragm cannot. In practice that advantage is mostly on paper: when a pressure tank fails at year 8 or 12, the switch, gauge, tee and often the shutoff want replacing too, and the whole assembly gets swapped whichever tank it is. Almost nobody replaces an air cell on a house tank.

Here is how a tank failure actually goes. The bladder or diaphragm ruptures, water displaces the air in the top of the tank, and the tank becomes waterlogged: the pump short-cycles, the pressure swings, and the switch clicks on and off while you run a faucet. If you tip the tank and it is heavy, it is full. At that point a plumber is at the house with a bill for labor already started. A new WX-203 package with the tee, switch and gauge is $1,295 shipped from us; a replacement air cell has to be ordered, the tank drained and opened from the top, the cell swapped and the tank recharged, and the old switch and tee are still old. Most plumbers, and most homeowners, put in a new tank. The feature is real; the money it saves is not.

Where the math might change is a large commercial or agricultural fiberglass tank in a wet location, where a replacement shell is expensive and the room is the reason you bought fiberglass in the first place. For a house, treat the rubber in either tank as a lifetime part and buy the tank with the longer warranty.

Ask Aidan

Not sure whether your tank location counts as "wet"?

Text me a photo of where the tank sits and of the old tank's bottom fitting. I'll tell you whether fiberglass is worth it there or whether a Well-X-Trol is the right call, and which size.

Text Aidan 443-277-2204 Call800-460-5810Aidan

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Size cross-reference: WellMate models and the Well-X-Trol that matches

Pressure tanks are not storage tanks. A "40 gallon" tank of either material holds about 10 to 12 gallons of usable water before the pump starts; the rest of the volume is air. Size to the pump, not the house, and compare tanks on drawdown, not total gallons. The table pairs each residential WellMate with the Well-X-Trol Pentair itself lists as the equivalent in its replacement guide, using each maker's published drawdown at a 30/50 switch (pump on at 30 psi, off at 50).

Two things to notice. Pentair's own replacement guide maps the WM-12 and the WM-14WB to the same Well-X-Trol, the WX-250, because on drawdown they bracket it. And the tall, skinny WM-12 (57 inches) needs more headroom than either the WX-203 (47 inches) or the squat WX-250 (36 inches); if the tank lives under a low floor, check the height before you check anything else. The WX-205 is the Well-X-Trol for spaces under 3 feet tall: 34 gallons, 10.5 gallons of drawdown, 30 inches high. For the sizing logic behind these numbers, see the pressure tank sizing guide.

Whichever material you choose, the tank comes first in line from the well and every treatment system installs after it: acid neutralizer, iron and sulfur filter, softener, UV. That order does not change with the tank material.

What to buy, and where

For a basement, utility room or heated garage, buy the Well-X-Trol WX-203 Pro Series. We sell it as a complete package, tank plus brass tee kit, pressure switch and gauge, for $1,295 shipped. For a well house, damp crawl space or coastal shed, buy a WellMate WM-12 or FlexLite FL-12 from a plumbing supply house. We used to stock WellMate and no longer do; the Well-X-Trol covers what nearly every caller actually needs, and I would rather send you to Ferguson or a local supply house for the fiberglass tank than sell you one you do not need.

When you compare prices, compare like for like. A tank-only price at a supply house does not include the tee, the switch, the gauge, the relief valve or the drain, and you should replace all of them with the tank; a switch that has cycled for 15 years is on the same clock the tank was. If the location is wet enough to justify fiberglass, the tee and switch have probably been corroding in it too. Our pressure tank cost guide breaks down what an installed replacement runs.

The four Well-X-Trol sizes we ship: WX-202 (20 gal, $1,095) for cabins and one-bath houses, WX-203 (32 gal, $1,295) for most homes on a 1/2 HP pump, WX-205 (34 gal, $1,695) where height is under 3 feet, and WX-250 (44 gal, $2,195) for 3/4 to 1 HP pumps, large households and irrigation. All are Pro Series with the stainless connection and 7-year warranty. The full set is in the well tank collection, and if you want the whole picture on how a tank works, sizing, air charge and troubleshooting, start with the complete guide to well pressure tanks.

Certified lab test, $199

Before you buy any treatment for the water: test it

One certified lab test, mailed to you, run by an accredited lab, shows the pH, iron and sulfur that decide what goes after the tank. Whichever tank you choose, this is what tells you whether you need a neutralizer or an iron filter behind it.

Get the certified well water test

53 contaminants. Results reviewed by Aidan, in plain English.

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