The correct answer would be 0.85 liters.

It can be explained with the help of unit rate that is, when the rate is expressed as the quantity of 1 for example, 5 meter per second, 5 liters per day et cetera.

In this case, unit rate (liter per day) can be calculated by dividing the total amount of water used by total number of days.

Amount of water used in 28 days = 23.8 liters

The amount of water used in one day = frac{23.8}{28}

It comes out to be 0.85 liters per day or 850 milliliter per day.