Last Updated on September 22, 2026 by Umar Farooq
It runs a short wash before the real one, then throws that water away. GE’s description is exact: the machine will “fill the Washer (adding the prewash detergent), tumble or agitate the clothes, drain and spin. Then, the Washer will run the selected wash cycle.” It is for loose, heavy soil — and it needs its own dose of detergent, in its own compartment.
That last clause is where most people lose the benefit. Select prewash, put detergent only in the main compartment, and the prewash runs on plain water and achieves nothing before draining away.
What does prewash do that a soak does not?
These two options sit next to each other on most machines and do genuinely different jobs, which GE separates cleanly.
Prewash is an extra wash cycle, “for use when clothes are excessively soiled.” It fills, agitates, and then drains and spins — so whatever it lifted leaves the machine before the main wash starts.
Soak holds the clothes in detergent and water without much movement. GE’s AutoSoak is “for use with most soaking aids to loosen embedded soils and stains”, and it “begins with a brief tumble or agitation and then proceeds to soak the clothes with water and detergent for a specified period of time” — adding “an additional 15 minutes, 30 minutes, 1 hour or 2 hours to the overall wash time” (prewash and AutoSoak cycles).
The distinction decides which one you want. Loose dirt that should leave the machine → prewash. A dried stain that needs time → soak. Running a prewash on a set-in stain mostly wastes water, because the soil was never going to release in fifteen minutes of agitation.
The compartment nobody fills
Look at your dispenser drawer. On most machines there are three compartments, and the prewash one is usually marked I while the main wash is II. GE is explicit that prewash detergent goes in “the prewash dispenser” — a separate dose from the main wash — unless you have a SmartDispense model that meters it for you.
Persil, which makes the detergent rather than the machine, gives the same instruction independently: “When you choose a prewash cycle, add detergent to both the prewash and detergent compartments of the dispenser” (how to choose the correct wash cycle).
Two consequences follow, and both are common.
The wasted prewash. No detergent in compartment I means fifteen minutes of agitation in plain water, then a drain. On genuinely muddy clothing that still does something — grit and loose soil go down the drain rather than into the main wash — but it is a fraction of what the option is for.
The blocked compartment. Because that compartment is rarely used, it is the one that collects dust, dried splashes and detergent that crept over the divider. The first time you finally use it, it may not flush properly. Which compartment is which, and what goes where, is in detergent drawer compartments explained.
When prewash is worth the water, and when it is not
It roughly doubles the water and time of the wash portion of the cycle, so it is worth being deliberate.
Use it for: mud and sand, nursery and farm clothing, workwear carrying grit or sawdust, anything where visible loose soil would otherwise circulate in the main wash and redeposit on everything else in the drum.
Skip it for: normal laundry, which is what the main cycle is designed for; and set-in stains, which want a soak or a hand pretreat instead. Skip it too if you are only adding it because the load “looks dirty” — that is what the soil-level setting is for.
One strong opinion: on a normal load, prewash is the least useful button on the machine. Its real value is narrow and physical — getting solid dirt out before the wash — and using it as a general upgrade just doubles your water bill on a load that was going to come out clean anyway. If your normal washes are not getting things clean, the dose is a more likely culprit than the cycle (how much detergent to use).
FAQ
What does prewash do on a washing machine?
It runs a short extra wash — fill, agitate, drain and spin — before the main cycle, so loose soil is flushed out of the machine rather than circulating in the main wash.
Do you need detergent for a prewash?
Yes, and it goes in the separate prewash compartment. Without it the prewash runs on plain water.
What is the difference between prewash and soak?
Prewash washes and drains away first. A soak holds the load in detergent and water for a set time without draining, which suits dried-in stains.
How long does a prewash add to a cycle?
Roughly the length of a short wash plus a drain and spin. GE quotes soak times separately at 15 minutes to 2 hours.
Which compartment is prewash in the drawer?
Usually the one marked I, with the main wash marked II. Check the symbols on your own drawer — layouts vary.
Is prewash worth using every time?
No. It roughly doubles the water for the wash portion and only earns that on genuinely dirty loads.
Use it for thick dirt, use soak for old stains
Prewash is a good answer to a narrow question: how do I get loose dirt out of the machine before the real wash starts. Fill the right compartment when you use it, leave it off the rest of the time, and reach for the soak option instead when the stain is old rather than thick.
