Richard
Is the house a Villa or Townhouse
If Villa he must have a private contractor looking after the rear gardens he should contact them, if a front garden, I believe the Entidad gardeners are responsible.
If a Townhouse, the gardens will be part of a community which is administered by Housing as long as it is not Phase 4
The community employs contractors who look after the sprinkler systems so you need to contact Housing or the President
Does he have a property manager/key holder?