Items like built-in hot tubs and ponds that are permanent structures, fixed to the grounds of your property, would be considered part of the building and included in the buildings section of your policy (where applicable).
Temporary structures in the open grounds of your home that could be easily moved around the garden, taken down or moved elsewhere would be included in the contents section of your policy. The level of cover ranges from £250 to £2500 depending on your insurance policy.
If you're unsure of the limits of your particular policy please don't hesitate to contact us.