water_mass_accounting_error = tendency_of_subglacial_water_mass -
  (tendency_of_subglacial_water_mass_due_to_input +
   tendency_of_subglacial_water_mass_due_to_flow +
   tendency_of_subglacial_water_mass_due_to_conservation_error +
   tendency_of_subglacial_water_mass_at_grounded_margins +
   tendency_of_subglacial_water_mass_at_grounding_line +
   tendency_of_subglacial_water_mass_at_domain_boundary);

water_mass_accounting_error@long_name = "subglacial water mass accounting error";