Table 4.
Comparison of log-reduction target (LRT) recommendations for onsite non-potable water systems.
| Water Use Scenario | Human Enteric Viruses | Parasitic Protozoa | Enteric Bacteria | |||
|---|---|---|---|---|---|---|
| 2021 LRT Update | 2017 LRT Guidance | 2021 LRT Update | 2017 LRT Guidance | 2021 LRT Update | 2017 LRT Guidance | |
| Untreated Onsite Wastewater | ||||||
| Unrestricted irrigation | 7.5 | 8.0 | 5.5 | 7.0 | n.d.c | 6.0 |
| Indoor use | 8.0 | 8.5 | 6.5 | 7.0 | n.d.c | 6.0 |
| Greywater | ||||||
| Unrestricted irrigation | 5.5 | 5.5 | 3.5 | 4.5 | n.d.c | 3.5 |
| Indoor use | 6.0 | 6.0 | 4.5 | 4.5 | n.d.c | 3.5 |
| Stormwater (10% wastewater contribution) | ||||||
| Unrestricted irrigation | 6.5 | 5.0 | 4.5 | 4.5 | n.d.c | 4.0 |
| Indoor use | 7.0 | 5.5 | 5.5 | 5.5 | n.d.c | 5.0 |
| Stormwater (0.1% wastewater contribution) | ||||||
| Unrestricted irrigation | 4.5 | 3.0 | 2.5 | 2.5 | n.d.c | 2.0 |
| Indoor use | 5.0 | 3.5 | 3.5 | 3.5 | n.d.c | 3.0 |
| Roof Runoff Water | ||||||
| Unrestricted irrigation | n/aa | n/aa | 1.0 | n.d.b | 1.0/0.0d | 3.5 |
| Indoor use | n/aa | n/aa | 1.5 | n.d.b | 1.5/1.0d | 3.5 |
a
Human enteric viruses were assumed to be not applicable in roof runoff.
b
The 2017 LRT Guidance did not determine protozoan LRTs for roof runoff due to lack of available data.
c
The 2021 LRT Update did not determine enteric bacteria LRTs for wastewater, greywater, or stormwater.
d
The 2021 LRT Update calculated enteric bacteria LRTs for roof runoff but did not recommend them; shown are values for Campylobacter/Salmonella spp.