A filter on the washing machine supply is a real and useful thing, and it protects the appliance rather than the washing. That distinction is worth making early, because most people searching for one are unhappy with how their laundry looks or feels, and the causes of that are hardness and iron, neither of which a filter touches.
What the filter genuinely does
A washing machine fills through small solenoid valves with fine internal passages and screens, and those are vulnerable to grit, rust flakes and pipe scale, particularly after plumbing work or on older pipework. A sediment filter on the feed keeps that material out and prevents the classic failures: a valve that will not close fully, a machine filling slowly, or an inlet screen silted up to the point where the appliance reports a supply fault. On well water it is a sensible fitting.
The complaints it will not fix
Stiff, grey washing that needs more detergent every year is hardness reacting with the detergent to form a residue that deposits in fibres. Orange or brown staining is iron. A chlorine smell in towels is the disinfectant in the supply. None of the three is a particle, so no sediment cartridge removes any of them. Fitting a laundry filter and expecting softer towels is the most common disappointment in this category, and the product descriptions rarely discourage it.
What each complaint actually needs
Hardness needs an ion exchange softener, and laundry is one of the first places people notice the change. The USGS classifies hardness as dissolved calcium and magnesium, soft at 0 to 60 mg/L as calcium carbonate through to very hard above 180, and the case for treatment strengthens with the band. Iron needs a softener within its limits or an iron filter above them. Chlorine needs carbon, usually as a point of entry stage since the showers benefit too.
Fitting one anyway
If the goal is protecting the appliance, fit a sediment cartridge on the cold feed with isolation either side, size it so it does not throttle the fill, and check the machine's own inlet screens at the same time, since they silt up quietly and produce identical symptoms. Choose a moderate rating rather than the finest available. Change it on a schedule, because a blocked filter is itself a cause of slow filling. Our whole house filter guide covers treating the laundry supply along with the rest of the house.
Questions people ask about laundry water filter
Will a laundry filter make towels softer?
No. Stiffness comes from hardness reacting with detergent, and hardness passes through any sediment filter. That needs a softener.
What does it actually protect?
The washing machine's inlet valves and screens, which are vulnerable to grit, rust flakes and pipe scale, especially after plumbing work.
What removes orange staining on washing?
Treating the iron in the supply, with a softener within its limits or an iron filter above them, rather than filtering at the appliance.
My machine fills slowly. Is that the water?
Check the machine's own inlet screens and any filter cartridge on the feed. A blocked filter causes the same symptom it was fitted to prevent.