Building permits for new buildings and building alterations shall be granted only if:
a.
in areas served by public sewers, polluted wastewater is discharged into the sewers (Art. 11 para. 1) or used for agricultural purposes (Art. 12 para. 4);
b.
outside areas served by public sewers, the appropriate disposal of polluted wastewater is ensured through special procedures (Art. 13 para 1); the cantonal water protection agency shall be consulted to this effect;
c.
there is a guarantee that wastewater which is unsuitable for treatment by a central wastewater treatment plant may be disposed of in an appropriate manner (Art. 12 para. 2).