Table 2.

Estimated log reductions in infectious Cryptosporidium and Giardia in drinking water supplies in Norway based on treatments in place and precipitation quantity.

Water treatment process	Cryptosporidium: approx. Log reduction	Giardia: approx. Log reduction
Coagulation/filtration (optimal)	2.7–3.1	3.1–3.6
Coagulation/filtration (during excess precipitation)	1.5	1.3
Membrane filtration	3–6	3–6
UV treatment (alone, optimal)	2–6	2–6
UV treatment (alone, during excess precipitation)	1.5–4	1.5–4
UV treatment (following filtration, during excess precipitation)	2–5	2–5
Coagulation/filtration and UV	Sum of individual values
Other (including groundwater supply)	0	0