Will water harvesting from air with the Sanakvo water harvesting technology reduce the chance of rain for a farmer 50 miles east of Sanakvo-Town with 10 million inhabitants?

Sanakvo has developed a new technology for harvesting drinking water directly from air. The technology is aimed at poor people living in arid regions without sufficient supplies of clean water. Sanakvo propagates and delivers this technology at a low cost, which does not need long distance piping or electricity. The frequently asked question is: Does this technology reduce humidity in the atmosphere and does this reduce the chance for rain or also for water harvesting in nearby regions?

We calculate the amount of water taken out of the atmosphere by use of the Sanakvo technology for a model city (SANAKVO-TOWN) under simplified but reasonable conditions and assumptions. We compare the amount of water harvested from the atmosphere with the amount of water present at any time over Sanakvo-Town and check for potential deficits.

Our assumptions

1. Wind blows all year from west to east

2. All inhabitants of Sanakvo-Town (10 million) use the technology

3. All people produce and use 10 l drinking/washing water per person per day.

4. Water from air is not used for irrigation of industry purposes (simplification for a start).

5. Total water harvest of Sanakvo-Town per day is = 10⁷ × 10 l = 10⁸ l total.

6. The area of Sanakvo-Town is 50 miles × 50 miles = 2 500 miles².

7. Low air cubus (1 mile altitude) over Sanakvo-Town: 2 500 miles³.

8. Relative water saturation in this cubus: 50 % (at least at night) all year round

9. Temperature in this cubus all year around: 30 °C (simplification for a start)

10. Amount of water per cubic mile under the above conditions: 16 g/m³ or 1.6 × 10¹⁰ g/km² or 6.67 × 10¹⁰ g/mile³.

Total amount of water in the 2 500 mile³ low air cubus at the above condition: 1.667 × 10¹⁴ g or 1.667 × 10¹¹ l water.

Questions

• How does the above low air cubus water amount compare with the water harvest of Sanakvo-Town?

  • Harvested water per day by Sanakvo-Town: 10⁸ l per day

  • Low air cubus water over Sanakvo Town at any time: 1,667 x 10¹¹ l

  • Only 0.06 % of the low air cubus water is taken out per day under the above assumptions.

  • If we would allow for a 100 l water harvest per day in Sanakvo-Town, water harvest would be 0.6 % of the low air cubus water.

• How does the net transport of evaporated water from oceans compare with the water harvest data from Sanakvo-Town?

  • Net transport rate of water from the oceans to the continents = 4 × 10¹⁶ l per year or 1.1 × 10¹⁴ l per day.

  • Water residence time in the atmosphere and water recycling time is only 9 days.

Conclusions

1. The water harvesting activity is irrelevant for the farmer 50 miles east of Sanakvo-Town since the low air cubus still contains 99.94 % of its original air bound water.

2. Even a water harvesting allowance of 100 l/person per day would also not result in relevant water deficits for our farmer east of Sanakvo-Town.

3. This statement is however only true if there is airflow over Sanakvo-Town, provided that the airflow is turbulent and not laminar.

4. Any loss of humidity due to precipitation (or water harvesting from air) on the globe is replenished by fresh humid air from the oceans. Water residence time in the air is 9 days.

5. Water deficit per day due to water harvesting from air from a 10 million population is 1 × 10⁸ l and compares to a net daily global transport of atmospheric water from the oceans to the continents of 1.1 × 10¹⁴ l.

6. Continuous wind is the most important factor which avoids conflicts with our eastward neighbors.

Literature

1. W. H. Schelesinger (1991), Biogeochemistry, Academic Press.
2. J. Grotzinger, T. H. Jordan, F. Press, R. Siever, Allgemeine Geologie (2008), Spektrum Verlag.
3. M. H. Schertenleib and H. Egli-Broz (2003), Globale Klimatologie.

2011-02-01 J. B.