Does organic cotton use less water than conventional cotton?

Question

In The Guardian's article Cotton production linked to images of the dried up Aral Sea basin, it's claimed that organic cotton uses less water than conventional cotton.

“Conventional cotton (as opposed to organic cotton) has got to be one of the most unsustainable fibres in the world,” says fashion designer and environmentalist Katharine Hamnett. “Conventional cotton uses a huge amount of water and also huge amounts of pesticides which cause 350,000 farmer deaths a year and a million hospitalisations.”

...

Hamnett advises another key step - phasing out conventional cotton and investing instead in its far more sustainable counterpart: organic cotton.

The environmental impact of losing the Aral Sea is not yet known, what we do know is that the cotton that destroyed it, is cotton picked by forced labour and destined for European shops. This is the reality of a subcontracted deregulated industry not bound by any global environmental or minimum wage legislation.

The article makes some claims that I regard as very serious and very plausible - that Soviet and post-soviet countries use forced labour in picking cotton (addressed here), and have ruined the Aral Sea.

However, I'm rather doubtful about their claim that organic cotton uses less water. The Guardian's biography of the article's author indicates that she has written about capitalism and fashion previously, and been involved in various political campaigns, but doesn't mention a university-level science education. The person being quoted, Katherine Hamnett, is a fashion designer and environmentalist, which is someone who cares about the environment but isn't necessarily a knowledgeable expert about the environment or farming. The article doesn't describe how organic cotton uses less water than conventional farming. Also, the article is funded by industry, though they claim that they retain editorial independence for this article.

It's plausible that some farmers of cotton may use less water than other farmers of cotton, but does organic cotton use less water than conventional cotton?

Answer 1

The claim that organic cotton farming uses less water than conventional modes of farming appears to be the scientific consensus. For instance, Grose (2009) states that

[farmers] in Israel have reported that cotton grown under organic conditions requires 30% less water than water in conventional systems […]. Organic cotton farmers in Texas have reported similar results.

You might find the wording here somewhat misleading. The advantage of organic cotton farming is not that the plants themselves require less water, but that water retention is greatly improved, and that the need for artificial watering can therefore be reduced quite notably. As Gomiero et al. (2011) summarize:

Soils in the organic system capture more water and retain more of it, up to 100% higher in the crop root zone, when compared to conventional. Such characteristics make organic crop management techniques a valuable resource in this present period of climatic variability, providing a better buffer to environmental extremes, especially in developing countries.

In a similar vein, Rieple & Singh (2010) conclude that organic cotton farming

has also been shown to make land easier to plough and retain water, helping crops to sustain periods of drought better. This appears to have been especially noticeable in those parts of India with heavy clay or sandy soils which are not normally usable for cotton because of their shallowness and low water retention

However, this advantage of organic cotton farming may disappear in areas where water scarcity is not an issue, e.g. because there is enough rainfall. Under those conditions where plants have to be irrigated in order to yield a profitable amount of cotton, organic cotton farming appears to be advantageous.

The Guardian's article talks about the question whether cotton farming is responsible for the disappearance of the Aral Sea. The Aral Sea is located in a climate zone with arid and semi-arid conditions, so the region might indeed profit from the better water retention capabilities of organic cotton farming. Conventional cotton farming has long been known to have a disastrous effect on the water levels in that region:

Thus, the Aral Sea disaster is the prime example for unsustainable irrigation development: rapid, large-scale expansion; sole reliance on high-water-use production systems for cotton and rice; poor water distribution and drainage; inefficient irrigation techniques resulting in enormous losses of irrigation water; and large-scale, non-dose-related uses of fertilizers and pesticides (Cai et al. 2003)

References

Cai, X., D. McKinney & M. Rosegrant. 2003. Sustainability analysis for irrigation water management in the Aral Sea region. Agricultural Systems 76(3), 1043–1006.

Gomiero, T., D. Pimentel & M. Paoletti. 2011. Environmental Impact of Different Agricultural Management Practices: Conventional vs. Organic Agriculture. Critical Reviews in Plant Sciences 30(1-2), 95–124.

Grose, L. 2009. Sustainable cotton production. In Blackburn, R. S. (ed.). Sustainable textiles. Life cycle and environmental impact. Boca Raton: CRC Press, 33–62.

Rieple, A. and Singh, R. 2010. A value chain analysis of the organic cotton industry: The case of UK retailers and Indian suppliers. Ecological Economics 69(11), 2292–2302.