As the erfdienstbaarheid suggests this refers to rights or an easement (or equitable servitude, if you prefer) concerning the land. The term "drainage easement" would probably cover "waterloop en drop", however for completion "watercourse and drainage easements" should perhaps be used, e.g.

" The number of housing units per acre of land, excluding public roads, natural watercourse and drainage easements, and other dedicated rights of way."

ref. http://www.scottsdaleaz.gov/generalplan/Glossary.asp