This standard cancels the previous parallel solution of DIN EN 1717 "Protection against pollution of potable water installations and general requirements of devices to prevent pollution by backflow - Technical rule of the DVGW" and DIN 1988-4. DIN 1988-100 shall be used only in conjunction with the DIN EN 1777 which was republished at the same time and provides explanations and information for the application of EN 1717 in Germany. They are planning and design tools as contained in DIN 1988-4, which could not be adopted into EN 1717:2001-05 for reasons of consensus. The relevant content of the standard covers information taken from the national annex NA of DIN EN 1717:2001-05 (backflow of used water, connection, external influences, materials, stagnation, harm caused by inadequate or improper maintenance, separation by single or double walls, point of use protection for equipment at the draw-off point). With respect to the previous national annex NA to DIN EN 1717:2001-05, the common protection (collector-unit backflow prevention) on risers, consisting of check valve and anti-vacuum valve type D or E according to DIN 3266-1 and DIN 3266-2 are no longer intended as protection units. Furthermore, the type of design A (corrosion protected) has been deleted without replacement for water heaters, and the other texts have been updated. The list in Annex A containing examples of protection units for domestic and non-domestic areas has been analogously assigned in descending order to the fluid categories of DIN EN 1717. The standard has been prepared by Working Committee NA 119-04-07 AA "Häusliche Wasserversorgung" ("Domestic water supply") of NAW.