A Whirlpool WHER25 membrane and a Whirlpool WHER25 pre-filter run on two separate clocks that almost nobody separates. The pre and post filters change every six months. The membrane runs a far longer stretch, and Whirlpool puts that stretch at one to two years.

Water Filters FAST stocks the WHEERM membrane at $69.99 and the WHEERF pre and post filter pair at $64.99. Both are in stock today.

A slow faucet sends most owners straight to the membrane. That is often the wrong part, and the reason is a design change Whirlpool made to the post-filter.

Written by the Water Filters FAST filter experts. Reviewed by Phil McNamara, owner, Water Filters FAST. Updated August 2026.

The orange tip explains a lot of slow faucets

Whirlpool updated the WHER25 pre and post filter set. The new post-filter carries an orange tip, and the Water Filters FAST listing carries Whirlpool's note about what that tip means.

The listing states that the updated filters carry certification to reduce forever chemicals. Denser media does that job. Denser media also slows the water down.

A WHER25 owner who installs the orange-tip set and then watches the faucet run slower has a system working exactly as designed. The flow drop is the price of the new certification.

Check the tip color before ordering a membrane. An orange tip installed in the last six months accounts for the slowdown on its own.

The two service clocks

Whirlpool sets six months on the pre and post filters. Those two cartridges catch sediment and chlorine before the water reaches the membrane, and they load up fast because that is their job.

The membrane runs longer. The Water Filters FAST set listing gives a range of one to two years depending on water conditions. The membrane listing calls a year typical and points at pH and hardness as the variables.

Hard water shortens the membrane. Soft water on a well with steady pH stretches it toward the two year mark.

Running the pre-filters past six months shortens the membrane too. Chlorine reaching a thin-film composite membrane damages it, and the pre-filter is the only thing standing between them.

What the WHEERM membrane is rated for

The Whirlpool WHEERM Replacement Membrane is a thin-film composite element. Water Filters FAST prices a single membrane at $69.99 and a 3 Pack at $189.99.

NSF and ANSI certified the WHEERM under Standard 58 for the reduction of total dissolved solids and organic matter. Its rejection rate runs 90 to 95 percent.

Rejection rate is the number that matters on an aging membrane. A membrane that used to strip 95 percent of the dissolved solids and now strips 70 percent still passes water. The water simply carries more of what the system was bought to remove.

Whirlpool also catalogs the membrane as WHEERM5, 129801, 652335, and 7296123. It replaces Kenmore 42-38577.

The membrane fits three Whirlpool systems. WHER25 owners, WHAROS5 owners, and WHAPSRO owners all buy the same element.

What the WHEERF pre and post filters do

The Whirlpool WHEERF UltraEase Under Sink Replacement Filters pack holds both cartridges. Water Filters FAST prices the pair at $64.99 and a 3 Pack at $179.99.

NSF and ANSI certified the WHEERF set under Standards 42 and 58 for sediment reduction and chlorine taste and odor reduction. The pre-filter takes the incoming load. The post-filter polishes the water on its way to the faucet.

Whirlpool catalogs the set as WHEERF5, WHEERF7, 129793, 652336, and 7296830. The listing states that WHEERF7 replaces WHEERF5. The set replaces Kenmore 42-38056.

One change from older sets deserves a mention. Whirlpool no longer includes the battery for the monitor, so an owner replacing a set on an older WHER25 supplies that separately.

Buying both parts together

Water Filters FAST sells a combined kit for the year the membrane comes due. The WHER25 pre and post filter set with membrane runs $119.99, down from a list price of $169.99.

The arithmetic favors the kit. Bought separately the two parts total $134.98. The kit takes $14.99 off that figure and ships as one box.

Buy the kit on the membrane year and the WHEERF pair alone at the six month mark in between. That pattern covers a WHER25 for its full service life.

Which systems and badges take these parts

Whirlpool built this reverse osmosis platform for several brands. The Water Filters FAST kit listing names every one of them.

Kenmore UltraFilter 450 and Kenmore UltraFilter 650 both take these cartridges. So do Kenmore Elite Premier reverse osmosis systems and any Whirlpool UltraEase reverse osmosis system.

The pre and post set also appears in big box parts catalogs as part 129793. Other retailers carry the same platform under their own house numbers.

A Kenmore owner holding a 42-38056 or a 42-38577 part number has found the right page. Those numbers map onto the WHEERF set and the WHEERM membrane.

How the three stages divide the work

A WHER25 treats water in sequence, and each stage removes what the next one cannot handle.

The pre-filter runs first. It strips sediment and chlorine out of the incoming line. Chlorine is the part that matters most here, because chlorine attacks a thin-film composite membrane and shortens its life.

The membrane runs second. It pushes water through a barrier fine enough to hold back dissolved solids and organic matter, and it sends the rejected water down the drain line. This stage is why a reverse osmosis system wastes water and why it produces slowly.

The post-filter runs last. Water leaving the storage tank passes through it on the way to the faucet, and it cleans up any taste the tank has added.

Skipping the pre-filter service damages the membrane. Skipping the membrane leaves the dissolved solids in the glass. Neither cartridge covers for the other.

What else slows a reverse osmosis faucet

Three causes account for most WHER25 slowdowns beyond the orange tip.

The storage tank comes first. A reverse osmosis tank holds its water against a bladder with an air charge behind it. That air leaks out over years, and a tank with a weak charge fills with water and has nothing left to push it back out.

House pressure comes second. A reverse osmosis membrane needs incoming pressure to push against. A house running under 40 psi produces water slowly no matter how new the membrane is.

A partly closed valve comes third. The tank valve and the feed saddle valve both get bumped during an under sink cleanout.

Work through those before spending money. The reverse osmosis collection carries tanks and fittings alongside the cartridges.

The order to replace parts in

Start with the cheapest check. Read the tip color on the post-filter and note the install date.

Replace the WHEERF pair next when six months have passed. Fresh pre-filters restore flow on a system that has simply gone too long between services.

Test the tank charge third. An empty tank should read about 7 psi at the schrader valve.

Replace the membrane last. A membrane that has run past two years, or a system whose water tastes like the tap again, has earned a new element.

Ordering and shipping

Water Filters FAST ships weekday orders the same day when they land before 1pm CST. Orders over $75 ship free, and both the membrane and the combined kit clear that line.

Returns run 30 days and a satisfaction guarantee backs every part. Browse the reverse osmosis membrane collection for other systems.

Call 855-789-FAST with the model stamped on the manifold when the numbers do not match anything above.

Frequently asked questions

How long does a WHER25 membrane last?

Whirlpool gives a range of one to two years on the Water Filters FAST kit listing, and the membrane listing calls a year typical. Water hardness and pH move the figure.

Why does a WHER25 slow down after new filters?

Whirlpool updated the post-filter with an orange tip and certified it to reduce forever chemicals. The listing states plainly that flow drops and water quality improves.

Do the pre-filters and the membrane change at the same time?

No. The WHEERF pair changes every six months. The membrane changes on a one to two year cycle, and the combined kit covers the year both come due.

Is the WHEERM the same as Kenmore 42-38577?

Yes. The WHEERM replaces that Kenmore part, and Whirlpool also catalogs it as 129801, 652335, and 7296123.

What does the WHEERM membrane cost?

Water Filters FAST lists a single WHEERM at $69.99 and a 3 Pack at $189.99. Both are in stock.

Will these parts fit a Kenmore UltraFilter 450?

Yes. The Kenmore UltraFilter 450 and 650 run the same Whirlpool platform and take the WHEERF set and the WHEERM membrane.

Order the WHER25 parts you need

Change the WHEERF pair on six months and the WHEERM membrane on its longer clock. Call 855-789-FAST or email support@waterfiltersfast.com when the tip color and the dates leave the answer unclear.