In some locations it is common for toilets, pits or tanks to be connected to storm drains which are covered and referred to locally as sewers. However, since the covering is often done informally with the covering being incomplete and/or not extending over the full length of the drain, they do not separate humans from excreta. Where used, this practice can therefore present a significant public health risk and for the purposes of the SFD, the excreta is considered NOT contained. Therefore when using the SFD Selection Grid, any toilet, pit or tank technology connected to an open drain, storm drain, storm sewer, or open sewer (covered or otherwise) should be classified as being connected "to open drain or storm sewer".