Weeping willow and most trees will send some roots down to 1 metre, and below, to draw up moisture but the bulk of the root system is contained as the root plate in the top 30-40cm.
How deep do rthe roots of a weeping willow go? We have geothermal heating loops in the garden at one meter depth and would like to plant a WW in a damp corner. Garden is large enough and will take a WW.
Geothermal loops are fully sealed and there is no possibility of roots penetrating them. The only other possibility for damage is by roots lifting the pipes, which might happen close to the surface as the diameter of the roots increased with growth, but not at 1 metre depth.