Moisture barrier on the floor slab

hello, I am currently building a house made of stone and I am laying a moisture barrier on the floor slab. now my "future" neighbor came by to see how far along I am with the house. he built a timber frame house last year and then told me that he did not install a moisture barrier. there is only tar paper laid under the walls. isn't a moisture barrier mandatory, or could that cause building damage? we already have groundwater at about 2-3m.

thank you

DIN 18195

Any masonry that comes into contact with moist ground must be protected against penetrating moisture. The damage potential of the surrounding soil varies, so a situation analysis must first be conducted before suitable protection is applied.

Often used is the so-called "black coating," a bitumen application. This building material has been commercially produced from petroleum since 1870 and is nowadays refined with polymers.

Although it is often suggested that waterproofing can be done by anyone, safety and guarantee are only ensured when tested professional companies carry out the work. The application is precisely defined in DIN 18195.