How many litres of water (how many showers) for a leather bag/a pair of leather shoes? (cow leather)

PART ONE: Raising cattle water use

(First note: 

Total water footprint of a 253 kg beef cow (in litres, assuming a total carcass weight of 143 kg as the report did) = 1,889,000L  
UNESCO-IHE: The Green, Blue and Grey Water Footprint of Farm Animals and Animal Products, page 28

The water footprint of raising cattle for leather is 17,100L of water per kg of leather. 

One cow produces 6.1kg of leather 

17,100L x 6.1kg per hide = 104,310L per hide 
UNESCO-IHE: The Green, Blue and Grey Water Footprint of Farm Animals and Animal Products, page 28

An average cow hide is 55sq ft (5.1sq m) 
Garrett Leather

104,310L per hide / 55 sq ft = 1,897.5L of water per sq foot of leather

An average pair of shoes requires 3 to 5 sq ft of leather (midpoint of 4 sq ft), 5 to 8 sq ft (midpoint of 6.5 sq ft) for boots 
Willy Moc Hand Crafted Shoes For Anyone, Russel Moccasin Co 

Pair of shoes: 4 sq ft * 1897.5L = 7,590L

Pair of boots: 6.5 sq ft * 1897.5L = 12,333.8L

The average American shower uses 15.8 gallons (59.8 litres) and lasts for 7.8 minutes at an average flow rate of 2.1 gallons per minute (gpm) (7.9 lpm).

The recommended shower length is about five minutes.
Home Water Works: Alliance for Water Efficiency, referenced March 2021

If we look at the recommended five minute shower (5/7.8 min * 59.8L) that’s 38.3 litres.

Therefore:

Pair of shoes: 7,590L/ 38.3L = ~198 showers 

Pair of boots: 12,333.8L / 38.3L = ~322 showers

Pair of shoes = 198 showers = a recommended 5 minute shower once a day for more than six months (198 / 30.4 days = 6.5 months) 

Pair of boots = 322 showers = a recommended 5 minute shower once a day for almost eleven months (322 / 30.4 days = 10.6 months) 

NOTE: This result alone should be phrased as ‘based on the water footprint of raising cattle for leather, an average pair of boots…’ as the above formula does not consider the amount of water wasted in the tanning of leather. This is good to use as people can’t claim ‘eco-tanning’

PART TWO: Tanning and finishing water use

‘The range of the specific water intake (SWI) for full tanning was found to be 170-550 L/hide.’
Water and Wastewater Management in the Tanning and Leather Finishing Industry: NATSURV 10 (2nd EDITION) Report to the Water Research Commission

Midpoint of range = (170 + 550) / 2 = 360L

1 leather hide = 104,310L (cattle raising) + 360L (tanning) = 104,670L 

 (4sq ft / 55sq ft) * 104,670L= 7,612.36L = 1 pair of shoes 

(6.5sq ft / 55sq ft) * 104,670L= 12,370.09L = 1 pair of boots 

Therefore:

Pair of shoes: 7,612.36L / 38.3L = 198.7 showers (almost 199 showers)  

Pair of boots: 12,370.09L / 38.3L = 322.9 showers (almost 323 showers) 

199 / 30.4 = 6.55 months of showering for a pair of shoes

323 / 30.4 = 10.63 months of showering for a pair of boots 

OR

Based on health recommendations advise drinking 2L of water per day
Health Line

Pair of shoes: 

7,612.36L / 2 = 3,806.18 days 

/ 365 = 10.4 years 

= Pair of shoes uses enough water for a person to drink for almost 10 and a half years

Pair of boots: 

12,370.09L / 2 = 6,185.05 days 

/ 365 = 16.95 years 

= Pair of boots uses enough water for a person to drink for 17 years 

1 leather hide = 104,310L (cattle raising) + 360L (tanning) = 104,670L

104,670/ 2 = 52,335 days 

/ 365 days = 143 years

One tanned leather hide is equal to the amount of water a human is recommended to drink (2L) for over 143 years

NOTE: the water use of leather tanneries likely varies from country to country based on the technology in place. For example, it is likely in India there is more water used, as perhaps there is not infrastructure to as effectively use and reuse water, as there is in South Africa, where this report is from. 

Additional calculations:

Using the same above data, alongside measurements for leather use in bags we can find out the water footprint of these accessories, too.

Bag leather requirements from e-mail correspondence with Sans Beast (0.914m2)

(9sq ft / 55sq ft) * 104,670L= 17,127.8L = 1 cow skin leather tote bag

DRINKING WATER:

17,127.8L / 2 = 8,563.9

/ 365 = 23.46 years