A strainer is a mesh screen in a housing that stops coarse material and is cleaned rather than replaced. It sits at the very start of a treatment train or immediately ahead of a vulnerable component, and it is doing a mechanical protection job rather than anything to do with water quality, which is the distinction that decides where it belongs.
What it catches
Sand, coarse grit, rust flakes, pipe scale, insects and the debris that appears after work on a main or a well. Those are the particles that score pump impellers, jam solenoid valves, wear valve seats and blind cartridges in days. Everything finer passes: silt, anything that makes water look hazy, and everything dissolved. So a strainer improves nothing about how water looks, tastes or measures, and protects a great deal that would otherwise be damaged.
Reusable rather than consumable
The screen is stainless or a durable polymer and is rinsed and refitted rather than thrown away, which is much of its attraction where the load is heavy. Some housings have a flush valve so the collected material can be blown out under pressure without opening anything, which is the spin down arrangement. Others have to be opened and the screen removed, which means isolation valves either side are worth fitting so a clean does not mean draining the house.
Where to fit one
First in the train, ahead of the pressure tank where the design allows, and certainly ahead of any cartridge filter, media vessel, softener or ultraviolet chamber. Immediately ahead of a pump, since grit destroys impellers and seals. On an irrigation line ahead of emitters. And after any plumbing work as a temporary measure, since cutting into old pipework lifts a season's worth of debris that would otherwise reach every fixture in the house.
Keeping it clear, and reading it
Clean or flush on a routine rather than waiting for a pressure drop, since a blocked screen becomes the restriction it was fitted to prevent. A clear housing makes that judgement easy and is worth choosing for that reason. And treat what accumulates as information: a screen filling within days on a well is telling you about the well rather than about filtration. Our whole house filter guide covers the finer stages behind it.
Questions people ask about water filter strainer
Is a strainer a filter?
Only in the mechanical sense. It stops coarse material to protect equipment and does nothing for taste, clarity or safety.
Does the screen need replacing?
No. It is rinsed or flushed and refitted, which is much of its attraction where the sediment load is heavy.
Where should it go?
First in the train, ahead of a pump and ahead of any cartridge, media vessel, softener or ultraviolet chamber.
How often should I clean it?
On a routine rather than waiting for a pressure drop, since a blocked screen becomes the restriction it was fitted to prevent.