Water Footprint: Green, Blue, and Grey Water

Water footprint accounting breaks down total freshwater use into green, blue, and grey components.

Understanding Water Footprint Components

Green water footprint refers to rainwater stored in the soil, which plants use through evapotranspiration. Blue water footprint involves the use of surface or groundwater, typically for irrigation, which is taken from freshwater bodies. Lastly, the grey water footprint represents the volume of water needed to dilute pollutants, such as fertilizer or pesticide runoff, to meet water quality standards.

In practical terms, fiber crops like cotton, hemp, and bamboo predominantly rely on green and blue water for their growth. The processing of these fibers—such as ginning, dyeing, and finishing—often results in additional grey water impacts due to chemical usage.

The chart above (Defra 2009) compares water (blue bars) and energy (red bars) needed to produce 1 kg of various raw fibers. Cotton (the leftmost blue bar) requires approximately 1,800 L/kg, significantly more than hemp (~200 L/kg) and linen (~150 L/kg). This disparity highlights cotton’s heavy irrigation and agrochemical demands.

In India, cotton's water footprint averages roughly 22,500 L/kg, while industrial hemp only requires about 2,719 L/kg. Bamboo-based viscose falls between 300–500 L/kg during its cultivation stage. These figures starkly illustrate cotton's excessive green/blue water use compared to the largely rain-fed hemp and bamboo.

Moreover, hemp and bamboo require substantially less fertilizer and pesticide. As noted, “agricultural inputs… are very low for fibers made from hemp, flax, [or] bamboo,” which dramatically lowers their grey-water burden.

Cotton Water Use in India

Cultivation

Cotton in India is one of the most water-intensive crops. The Water Footprint Network reports an astonishing average of ~22,500 L of water required for every kg of lint cotton in India, which is more than double the global average of ~10,000 L/kg. This situation arises because India's arid cotton regions—such as Punjab and Haryana—are heavily reliant on irrigation.

In fact, northwest India (Punjab, Haryana, Rajasthan) almost exclusively grows cotton through irrigation. By contrast, rainfed cotton in regions with higher precipitation, like Maharashtra or Telangana, uses far less water. Thus, cotton's blue water footprint is especially pronounced in India's cotton belt. In total, over 80% of cotton's water usage in India is attributed to irrigation.

Processing

The processing of cotton fibers includes ginning, spinning, dyeing, and finishing, all of which require additional freshwater for machinery cooling, sizing, scouring, and dye baths. A rough estimate suggests that around 100–150 L of water is needed for processing every kg of fiber.

Modern dyehouses significantly add to the grey water footprint from their chemical effluents. In India’s textile industry, recognized as a major dyeing hub, as much as 20% of industrial wastewater is generated from fabric processing.

Regional Variation

Cotton yields and irrigation demands vary by region. In Punjab and Haryana, intensive irrigation through canals or tube wells supports high cotton yields, but drains groundwater resources. In contrast, in states that receive more rainfall—like Andhra Pradesh and Odisha—cotton can be grown partly or entirely using rainfed methods, thus shifting to more green-water use. State averages illustrate this difference, such as ~5,000 m³/ton green and ~4,000 m³/ton blue in Maharashtra versus ~3,000 m³/ton green and ~10,000 m³/ton blue in Punjab.

Globally, cotton accounts for approximately 25% of pesticide use, further amplifying its grey footprint through fertilizer runoff.

Hemp Water Use

Hemp (Cannabis sativa) is an industrial crop that demonstrates much lower water requirements. Studies estimate that hemp’s water footprint is around ~2,719 L per kg of harvested biomass, roughly one-quarter that of cotton. The crop flourishes in moderate rainfall conditions of 500–700 mm/year and usually does not require irrigation in temperate climates due to its deep root systems.

In India’s hilly regions, such as Uttarakhand and Himachal Pradesh, annual precipitation is often sufficient for hemp's growth. However, in drier lowland areas, like Madhya Pradesh and Maharashtra, supplementary irrigation may be necessary.

Processing Hemp

Hemp fibers undergo extraction through retting and decortication. Traditional dew-retting relies on rainfall and microbial action in the fields, requiring virtually no additional water. Though water-retting (submerging stalks in water) is an option, it occurs less frequently and can produce significant effluent.

Once retted, hemp fibers are separated with dry processing methods, using little water compared to the ginning processes of cotton. The spinning and weaving of hemp yarn follow similar patterns, requiring 100–150 L/kg of fiber, and dyeing processes have similar water requirements. Notably, hemp cultivation generally uses minimal fertilizers or pesticides, resulting in a smaller grey-water footprint than cotton.

Uses of Hemp

In India, hemp primarily finds applications in textiles, paper, rope, and insulation materials such as hempcrete. The production of hempcrete uses water mostly for mixing with lime or resin, which is negligible compared to the water footprint during the cultivation stage.

Bamboo Water Use

Cultivation of Bamboo

Bamboo is a fast-growing grass primarily found in India’s northeastern and hilly regions, where it benefits from monsoon rainfall. Optimum bamboo species generally require ≥1,000 mm/year of rainfall, though some hardier varieties can survive with as little as 750 mm.

Bamboo plantations in high-rainfall areas like Assam and Meghalaya do not usually require additional irrigation. In contrast, in drier zones of western or central India, some irrigation might occur, although bamboo is often planted within agroforestry systems that capitalize on remaining soil moisture. Bamboo’s ability to regenerate quickly allows for the reforestation of previously used land, enhancing overall water infiltration and reducing runoff.

The farming footprint of bamboo is exceptionally low. One textile industry source indicates that regenerated fibers, such as bamboo, need only between 300 and 500 liters of water to grow 1 kg of raw material. This primarily consists of rainwater; once established, irrigation is seldom needed. Mechanical bamboo fibers can also be produced in rainfall-only systems.

Processing of Bamboo

The term "bamboo fabric" usually pertains to bamboo viscose rayon, rather than purely mechanical fiber. Producing viscose requires pulping bamboo (often with chemicals, such as sodium hydroxide) and spinning regenerated cellulose. A Water Footprint Assessment shows that viscose fiber has a footprint of around ~3,000 m³ per tonne (≈3,000 L/kg) of yarn, primarily due to chemical usage and wastewater management.

Thus, producing bamboo viscose significantly adds to the blue and grey footprint beyond the cultivation stage. In contrast, mechanically extracted bamboo linen (a process practiced in Kerala) avoids most chemicals, but yields less than 5% fiber by weight and is not industrially scaled in India.

Additional Uses

Beyond textiles, bamboo is utilized whole in various applications, such as poles and mats. These uses generally avoid the viscose stage, so their water footprint mainly reflects cultivation plus minor manufacturing requirements, such as adhesive preparation.

In summary, bamboo's total water use remains low when chemical processing is avoided.

Comparative Water Footprint Tables

The table below summarizes water footprints (green + blue) per kilogram of raw fiber and per m² of fabric (assuming 150 g fiber/m²) for cotton, hemp, and bamboo in India:

Fiber	Water footprint (L/kg fiber)<br>(green+blue)	Water footprint (L/m² fabric)<br>(150 g/m² assumption)
Cotton (India)	~22,500 L	~3,375 L/m² (i.e. 22,500 L/kg × 0.15 kg)
Cotton (global avg.)	~10,000 L	~1,500 L/m²
Hemp (industrial)	~2,719 L	~408 L/m²
Bamboo (bast/viscose)	300–500 L	45–75 L/m²
Bamboo (viscose fiber)	~3,000 L	~450 L/m²

Table: Green+blue water footprints of raw fiber and equivalent fabric area. Cotton’s Indian footprint is exceptionally high due to irrigation, while hemp’s footprint is an order of magnitude lower. The "bamboo" mentioned here refers to the plant itself, with the 300–500 L figure referring to rainfall-based growth of bamboo biomass. However, converting bamboo to viscose fiber adds around 3,000 L/kg to the total water use.

Regarding textile processing (spinning, weaving, bleaching, dyeing), an additional 100–150 L of water is generally required for every kg of fiber. These processing waters are largely independent of fiber type but significantly influence the final fabric footprint. For instance, a dyed cotton fabric uses its cultivation water plus an additional ~150 L/kg in the finishing stage.

Irrigation and Regional Context in India

Cotton irrigation has a profound impact on regional water use. In Punjab and Haryana, cotton-centric farming relies heavily on groundwater and canal sources, constructing an unsustainable water situation. Conversely, hemp is cultivated primarily in wetter, northern states like Uttarakhand (average ~1,150 mm rainfall) and Himachal Pradesh (approximately ~1,200 mm), where rainfall is usually sufficient.

In areas like Madhya Pradesh and Maharashtra—with 600–1,000 mm of rainfall—hemp often requires supplementary irrigation to thrive. Bamboo cultivation, especially in India’s high-rainfall zones, flourishes in places like Assam (receiving ~2,400 mm) and parts of West Bengal (around ~1,300 mm in certain areas).

Overall, cotton's cultivation increasingly overlaps with water-scarce areas, whereas hemp and bamboo are typically grown in regions with sufficient rainfall. Growing hemp or bamboo could help transition fiber production to less irrigation-dependent areas, reducing the pressure on over-exploited aquifers.

Environmental Trade-Offs and Industrial Viability

• Cotton: This well-established textile commodity yields high returns (2-3 tons per hectare). Its enormous water demand, however, strains vital resources and contributes to soil salinization plus pesticide runoff. While water-efficiency strategies, like drip irrigation and mulching, can assist, widespread adoption remains necessary. Cotton is a mature industry with ready infrastructure (ginning mills, spinning facilities, global supply chains). However, its grey footprint from fertilizers and pesticides is considerable. Cotton's scalability is validated, but sustainability relies on enhanced water stewardship and shifts toward organic or Better Cotton Initiative (BCI) practices.

  
  

• Hemp: Hemp’s extremely low water and chemical needs present an environmentally appealing alternative. Its deep roots contribute to soil health and erosion control. Moreover, it can often be rain-fed, particularly in upland regions of India. Nonetheless, developing a robust processing infrastructure is essential, as India currently possesses limited decortication and retting facilities. Initiatives aimed at building a hemp textile industry will necessitate investing in machinery for fiber processing and market development for co-products. The regulatory landscape for hemp, gradually relaxing THC restrictions, further enhances its industrial viability. In non-textile uses, such as hempcrete and automotive composites, the opportunities are promising but not yet widespread in India. Ultimately, the trade-off for hemp lies in initial investment versus significant water savings and reduced carbon emissions in the long run.

  
  

• Bamboo: Bamboo presents advantages as it grows rapidly on marginal land with minimal input requirements, offering benefits like carbon sequestration and watershed protection. Though mechanical bamboo linen can conserve water, it is labor-intensive and rare. Most commercially available “bamboo” textiles are viscose; the process of turning bamboo pulp into rayon can undermine its cultivation advantages due to high water and chemical usage. In India, while technical bamboo yarns often get imported, local endeavors, such as Tanboocel fiber, are still emerging. Therefore, bamboo’s industrial viability varies: as a raw material for poles, mats, and charcoal, it enjoys widespread use while facing challenges when competing as a virgin textile fiber.

  
  

• Non-Textile Applications: Both hemp and bamboo excel in various technical applications. Hempcrete and insulation materials utilize minimal fresh water in their production process. In addition, biocomposites (formed from hemp hurd or bamboo fiber) require similar processing methods as wood composites, which consume little water. Thus, water use for these applications primarily arises at the cultivation stage. In numerous scenarios, replacing cotton with hemp or bamboo fibers—like substituting hemp composites for glass fiber—can lead to a notable reduction in water impacts while also providing technical performance benefits (e.g., thermal insulation, durability).

  
  

Implications for Sustainable Sourcing

These comparisons offer critical insights for Indian textile and material industries: substituting cotton with hemp or bamboo could significantly reduce water usage by 80–90% per fiber unit. Decision-makers must assess this against market readiness. For example, converting conventional cotton acreage to hemp in Uttar Pradesh could save billions of liters annually, but this shift necessitates the establishment of new supply chains (from seed to textile). Brands utilizing Indian cotton could mitigate water risks by diversifying into hemp fabric to meet sustainability goals.

Key considerations include:

• Water Risk: The cotton farming methods in Punjab and Haryana pose serious hydrological challenges. Transitioning acreage to hemp or bamboo in more rainfall-rich regions can substantially lessen irrigation needs and offer protection against climate variability.

  
  

• Infrastructure Needs: Investment in retting and decortication facilities for hemp, as well as bamboo pulp mills using closed-loop systems, is vital. Public incentives or public-private partnerships (PPPs) can help fast-track this transition.

  
  

• Quality and Demand: Hemp fabrics currently differ in feel from cotton; consumer education and leveraging blends (like hemp-cotton blends) can help ease market adoption. Bamboo viscose competes with cotton in softness but must guarantee sustainable production methods (such as lyocell-like processes).

  
  

• Ecosystem Benefits: Beyond reduced water footprints, both hemp and bamboo contribute to soil remediation, biodiversity enhancement, and carbon sequestration. Such benefits align with ESG (Environmental, Social, and Governance) goals.

  
  

Conclusion: Examining the lifecycle of fiber cultivation exposes cotton's exceptionally high water footprint in India, mainly due to irrigation and agrochemicals. Hemp and bamboo, cultivated in suitable climates, require significantly less water and inputs. Transitioning to these alternative fibers in textiles and technical materials can drastically decrease the sector’s freshwater demand. The challenge remains in developing scalable and economically viable processing infrastructures for both hemp and bamboo. Indian industry must weigh short-term costs against the imperatives of long-term water security and sustainability. Prioritizing low-water fibers and enhancing irrigation efficiency enables manufacturers to mitigate water risks and support India’s sustainable development objectives.

FAQs: Water Footprint of Cotton vs. Hemp and Bamboo

1. What is meant by "water footprint" in the textile industry?

The water footprint quantifies the total freshwater volume used throughout the lifecycle of fiber—from cultivation (green and blue water) to processing and pollution (grey water). It encompasses rainwater use (green), irrigation (blue), and water needed to dilute chemicals and pollutants (grey).

2. Why is cotton considered a water-intensive crop in India?

Cotton demands significant irrigation in India, especially in arid regions like Punjab and Haryana. The crop also consumes large amounts of pesticides and fertilizers, contributing to a high grey water footprint. On average, producing 1 kg of cotton fiber in India requires over 22,500 liters of water.

3. How does hemp compare to cotton in terms of water usage?

Hemp uses approximately 80–90% less water than cotton. With its deep roots and minimal input needs, it typically thrives on rainwater alone in regions like Uttarakhand. Its cultivation footprint is about 2,700 L/kg, with little water necessary for processing.

4. Is bamboo truly a sustainable alternative to cotton?

Yes, especially when cultivated and processed responsibly. Bamboo requires little to no irrigation in high-rainfall regions, with water usage around 300–500 L/kg. However, bamboo viscose, frequently found in textiles, may incur higher water and chemical impacts unless produced with closed-loop systems.

5. What stages of the fiber lifecycle contribute most to water footprint?

In cotton, cultivation (primarily due to irrigation) is the significant contributor. In contrast, for bamboo and hemp, cultivation water usage is low. However, chemical-intensive processing (especially for viscose bamboo) can dramatically increase the total water usage and pollution load.

6. What are the grey water implications for each fiber?

Cotton has a notoriously high grey water footprint resulting from fertilizer and pesticide runoff, while hemp and bamboo generally maintain lower grey footprints due to requiring fewer agrochemicals. Nevertheless, the production of bamboo viscose involves effluents unless managed through closed-loop systems.

7. Are there regional advantages in India for growing low-water fibers?

Yes, hemp grows effectively in hilly, rain-rich areas like Uttarakhand and Himachal Pradesh, while bamboo thrives in Northeast India, Odisha, and Western Ghats. These locations minimize reliance on irrigation, unlike the cotton belts that excessively deplete groundwater.

8. Can hemp and bamboo fully replace cotton in textiles?

Not fully, but they can supplement and diversify fiber sourcing. Cotton remains dominant due to mature infrastructure and global demand, yet blends (e.g., hemp-cotton) and strategic bamboo use in technical applications present viable low-water alternatives.

9. What are the implications for non-textile applications?

Hemp and bamboo excel in technical uses, such as hempcrete, insulation, and composites, requiring minimal freshwater. These applications bypass water-intensive processing stages, making both fibers particularly sustainable. In most cases, substituting cotton with hemp or bamboo significantly reduces water impacts while offering additional technical benefits.

10. How can manufacturers reduce water footprint across fibers?

• Transition sourcing to low-water crops, like hemp or bamboo.

• Invest in closed-loop processing systems for viscose production.

• Emphasize organic or BCI-certified cotton.

• Implement water recycling and effluent treatment solutions in dye houses.

• Promote blended fabrics and local fiber supply chains.