Stiff Steering

[Devon]

Can anyone suggest what to check to improve my steering please?
I have to overcome some resistance whenever adding small steering inputs. It's not just from 'straight ahead' but from any steering angle. It's just stiff and resistant to moving. It is fine to continue steering once started but starting is stiff.
Down country lanes it doesn't trouble me because I'm always adding moderate steering inputs. However, on motorways when I want to add regular small inputs, it drives me absolutely crazy.

Could it be something as simple as low power steering fluid? Is that a thing? Is there a reservoir? 

2010 Forester X
EJ204JSYMB
UK

[Greenmamba]

Could be low power steering fluid amongst other possible causes including wheel alignment, low tyre pressure, failing steering rack/pump. Reservoir is likely to be on the right hand side (from the drivers perspective) of the engine bay.

[PeterH]

I have a similar problem - more prevalent on hot weather?? - steering stiffens up - in fact you could let go and it will stick to the position you are pointing in until you intervene?? I am suspecting my rack or the pump - did you ever resolve yours?