Water enters and leaves a human body, in an average day, as shown in the followi

Question

Water enters and leaves a human body, in an average day, as shown in the following figure and according to the following water percentages in some of the exchanges: food (70%), urine (99%), feces (74%), breathing in air (9%), and exhaling out air (41.5%).  
- Which equation would you use to estimate the quantity of water accumulated in the body? Explain.
- Define the different components of the water mass equation.
- Calculate the net gain (or loss) of water mass in this situation.

Food in 1500g, Air in 400g, Drinking water in 1200g,

Air out 1000g, sweat out 200g, Urine out 1200g, Feces out 300g, Evaporation of water through skin 350g

Explanation / Answer

Mass balance equation is used to estimate the quantity of water accumulated in the body is given below:

Massin + Massgenerated – Massout – Massconsumed = Mass accumulated                                                                  (1)

The different components of water mass equation are as follows:

To calculate Mass of water in

Food intake = 1500 g,

Weight% of water in food intake = 70%

Actual Weight of water intake by food = 1500 *70% = 1050g.

Similarly for air,

Air Intake=400g

Water % in Air=9%

Actual Weight of water intake by Air=400*9%=36g

For Drinking Water,

Actual weight of water intake by drinking water would be considered 100% i.e. 1200g

Hence total water intake = 1050+36+1200=2286g

To calculate Mass of Water Out

Air going out = 1000g

% of water in Air Going =41.5%

Actual water out by Air= 1000 * 41.5%=415g

Likewise for Sweat, water out is 100% therefore actual water out by sweat is 200g.

Similarly for urine, water out is 99% therefore actual water out by urine is 1200*99% = 1188g

Likewise for feces, water out is 74% therefore actual water out by feces is 300 * 74% = 222g

As Mass of water evaporated through skin is given as 350 g and it is assumed to be 100% therefore actual water out through evaporation is 350g.

As Mass of water generated and consumed= 0,

To calculate the net gain or loss of water mass, we have to use the equation (1):

1050+36+1200+0-415-200-1188-222-350-0= Mass accumulated

Thus, mass accumulated is -89g, which shows that there is net loss of 89g of water during the whole process.

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