40 CFR §142.304

1. (a)A small system variance is not available under this subpart for a national primary drinking water regulation for a microbial contaminant (including a bacterium, virus, or other organism) or an indicator or treatment technique for a microbial contaminant.
2. (b)A small system variance under this subpart is otherwise only available for compliance with a requirement specifying a maximum contaminant level or treatment technique for a contaminant with respect to which;
   1. (1)a national primary drinking water regulation was promulgated on or after January 1, 1986; and
   2. (2)the Administrator has published a small system variance technology pursuant to Section 1412(b)(15) of the Act.