There are two ways to get filtered water out of an outside tap, and they are not variations of the same idea. One is a small filter at the tap itself, serving that outlet only. The other is a whole house filter upstream, which serves the outside tap along with everything else. Which is right depends on what the outdoor water is for.
Why outside taps are usually left unfiltered
Standard practice on a whole house installation is to branch the outside tap off ahead of the filter, and the reasoning is simple: irrigation is the largest volume a household uses and treating it consumes cartridge capacity for no benefit, since plants and lawns do not care. A garden fed through the house filter shortens every cartridge interval considerably. So if the outdoor use is watering, the correct answer is usually no filtration at all rather than either of the options here.
When a tap mounted filter is right
Where a specific outdoor use needs it and the volume is modest. Filling ponds and aquariums needs chlorine removed, since it harms fish and the biological filter. Drip irrigation and misting lines need sediment removed, since the emitters block on particles too small to see. Pressure washers and sprayers need sediment removed to protect pumps and nozzles. Livestock troughs benefit from carbon. All of those are served far more cheaply by a hose filter than by treating the whole property.
When the whole house answer is better
Where the outdoor tap is used for drinking water, filling tanks or a summer kitchen, and where the property has sediment problems affecting every fixture anyway. A whole house filter also removes the seasonal chore of draining and storing an outdoor housing before frost, since the filtration lives indoors where it cannot freeze. If the property is on a well producing grit, whole house sediment removal is being fitted regardless and the outside tap can simply be taken after it.
Practicalities at the tap
An outdoor housing must not be left full of water over winter, because freezing splits it and the failure appears as a soaked wall on the thaw. Drain it, remove the cartridge and store it dry. Support the housing on a bracket rather than letting a full canister hang on the tap thread, since the leverage of a charged hose works the connection loose over a season. And use a potable rated hose if any of the water is going to be drunk. Our whole house filter guide covers the upstream option.
Questions people ask about water filter for outside hose
Should my outside tap be on the whole house filter?
Usually not. Irrigation is the largest volume a household uses and treating it consumes cartridge capacity for no benefit.
When is a filter at the outside tap worth it?
For ponds and aquariums needing chlorine removed, and for drip irrigation, pressure washers and sprayers needing sediment removed.
Can an outdoor filter stay out over winter?
Not full of water. Freezing splits the housing. Drain it, remove the cartridge and store it dry until spring.
Is hose water safe to drink through a filter?
Only through a potable rated hose. An ordinary garden hose contributes what the filter upstream of it cannot remove.