Biochemical Oxygen Demand (B.O.D.) of safe drinking water must be:

Agreed with Mr. Alex

Thanks

Around the figure of

1: zero

i am nt sure, bt zero should be safer, however practically its not possible

they say no more then3 parts on100.000 so that's is close to ZERO

Option 1: zero

Biological Oxygen Demand (BOD) : BOD is typically reported as5 day BOD and ultimate BOD at20 C and reported as milligrams of oxygen consumed per liter (mg O/L). BOD5 is used by regulatory agencies for monitoring waste water treatment facilities and monitoring surface water quality. BOD is the biochemical oxygen demand of the water and it is related to the concentration of the bacterial facilitated decomposed organic material in the water. A sample with a5 day BOD between1 and2 mg O/L indicates a very clean water, 3.0 to5.0 mg O/L indicates a moderately clean water and >5 mg O/L indicates a nearby pollution source. BOD is a laboratory test that requires a oxygen sensing meter, incubator, nitrifying inhibitors, and a source of bacteria. 

A BOD level of 1-2 ppm is considered very good.

DO is measured either in milligrams per liter (mg/L) or "percent saturation." Milligrams per liter is the amount of oxygen in a liter of water. Percent saturation is the amount of oxygen in a liter of water relative to the total amount of oxygen that the water can hold at that temperature.

Most pristine rivers will have a5-day carbonaceous BOD below1 mg/L. Moderately polluted rivers may have a BOD value in the range of2 to8 mg/L. Municipal sewage that is efficiently treated by a three-stage process would have a value of about20 mg/L or less. Untreated sewage varies, but averages around600 mg/L in Europe and as low as200 mg/L in the U.S., or where there is severe groundwater or surface water Infiltration/Inflow. (The generally lower values in the U.S. derive from the much greater water use per capita than in other parts of the world.)

Zero  0                                                                                                  .

Biochemical oxygen demand of water .if it is between1 to2 mg then it is clean form and if it is between3 to5 mg is moderate clean.