The current global population is 7.7 billion people, and the WHO estimates the minimum water need per person per day is 15 L. An estimate of accessible freshwater available as groundwater, lakes, and rivers is 6.34 x 100 km². How long will this water sustain the current population? Does the annual terrestrial precipitation meet the drinking water needs? If not, where might additional drinking water come from. A liter of water is 1 x 10-km².

a) The amount of freshwater available as groundwater, lakes and rivers, does not even reach one day the need for consumption for the current global population. (t = 5.489 E-13 day)

b) The annual terrestrial precipitation, reaches to sustain the drinking water needs for the current global population

Explanation:

Let P = 7.7 billion people = 7.7 E12 person

∴ water needed for the total population for one day:

⇒ water amount = 7.7 E12 person * (15 L / person. day) = 1.155 E14 L H2O / day

⇒ water amount = 1.155 E14 L H2O/day * 1 E1 Km² H2O / L H2O = 1.155 E15 Km² H2O/day * (365 day / year) = 4.216 E17 Km²/year

∴ freshwater available:

freshwater = 6.34 E2 Km² H2O

how long will this water sustain the current population?

⇒ t = 6.34 E2 Km² * day / 1.155 E15 Km² = 5.489 E-13 day

this amount of freshwater does not even meet the need of the current global population.

∴ the annual terrestrial precipitation (Py) = 505000 Km³/year ... from literature

⇒ Py = 505000 Km³ H2O/year * (1000 m/Km) ³ * (1000L/m³)

⇒ Py = 5.05 E17 L H2O/year * (1 E1 Km² / L) = 5.05 E18 Km² H2O/year

⇒ Py > water amount

the annual terrestrial precipitation of water, reaches to sustain the drinking water needs.