The Q is: how much conversion?

Nitrate is a health hazard because of its conversion to nitrite. Once ingested, conversion of nitrate
to nitrite takes place in the saliva of people of all age groups, and in the gastrointestinal tract of
infants. Infants convert approximately double, or 10 percent of ingested nitrate to nitrite
compared to 5 percent conversion in older children and adults.

What about bacteria?

http://des.nh.gov/organization/commissioner/pip/factsheets/ard/documents/ard-ehp-16.pdf