It is hard to imagine but somehow a cotton t-shirt costs 1220 liters of water, and 2 m2 of crop area. Here is how.
It is good way, to imagine how seeds become a t-shirt, to understand the real cost of textile products.
Here is an article to dig into. Average read 10 minutes.
Choosing the product to analyse…
We choose a basic t-shirt from amazon best sellers to generalize our meaning of cotton t-shirt. So, its weight is 200gr, and made of %100 cotton.
We will use this parameters for our calculations,
Important Notice;
Cotton is still the most important textile fiber with %25 market share in total fiber consumption. It is natural, and still – after many new fiber inventions, still-, the most comfortable and healthy option for human skin.
https://www.statista.com/statistics/741296/world-fiber-consumption-distribution-by-fiber-type
Cotton as a crop.
Main ingredients,
- Land
- Seed
- Time
- Sun Shine
- Water
Facts,
1.000 kg of cotton crop is grown in total of 2.000 m2 of crop area, in 180 – 195 days depends on weather conditions.And, during this period approximate water usage of 1.000 kg cotton crop is 1200 m3.
How we calculated,
A rainfall of 1 mm supplies 0.001 m3, or 1 litre of water to each square metre of the field. Thus 1 ha receives 10 000 litres.
600 mm = 0,600m ( cotton seed need ), 180-195 days, sun shine, 0,2 ha = 2000 m2 = 1000 kg of cotton ( before ginning )
2000 m2 x 0,600 m = 1200 m3 water = 1000 kg of cotton = 400 kg industrial cotton ( after ginning for yarn manufacturing )
QUESTION
What is the total amount of water received by a field of 5 ha under a rainfall of 15 mm?
ANSWER
Each hectare (10 000 m2) receives 10 000 m2 x 0.015 m = 150 m3 of water. Thus the total amount of water received by the 5 hectares is: 5 x 150 m = 750 m
Rainfall is often expressed in millimetres per day (mm/day) which represents the total depth of rainwater (mm), during 24 hours. It is the sum of all the rain showers which occurred during these 24 hours.
Details of calculation based on studies given below;
http://kisi.deu.edu.tr//cem.cetinkaya/sulama/CROPWAT8_0Example.pdf ( Cotton Crop, page 48 )
http://www.fao.org/3/r4082e/r4082e05.htm ( RAINFALL AND EVAPOTRANSPIRATION )
Cotton as a textile fiber.
Ginning process,
Cotton is ginned in 3 ways so far, Saw Gin, Roller Gin, and latest Rotobar. Average efficiency of these methods are %40.
What it means, it means that 1.000kg of cotton crop becomes 400 kg industrial cotton.
General information about cotton growing from WWF,
http://d2ouvy59p0dg6k.cloudfront.net/downloads/cotton_for_printing_long_report.pdf
For cotton statistics 2020,
https://www.statista.com/statistics/259392/cotton-production-worldwide-since-1990/
Spinning,
There are many spinning methods, right now with the improvement in yarn production technologies. We used to have only ring spinning, before the invention of rotor spinning. ( a detailed article about yarn technologies will be coming soon )
In our study, we use combed cotton ring spun yarn as our yarn, and it will be knitted for becoming a fabric.
Average thread/yarn waste% in fabric production is 5%
Average fabric waste% in t-shirt production is 18%
Average water waste for dyeing 1 kg cotton yarn/fabric is 120 litres.
As a result; 1.000 kg of cotton crop turns into app. 200 kg of t-shirts after all process. And, app. 1220 m3 of water consumed totally.
As a result,
We can say that 1 Cotton T – Shirt costs us approximately 1.220 litres of water, and lots of energy. And, a question;
1000 kg of seed-cotton turn into 200 kg of T-shirts, and what happens to 800 kg?
Suggested study.
https://ourworldindata.org/water-use-stress