Two ways to count it
You can count the water that goes into the device, or the water behind every phone charge it gives you over its life. They tell different stories.
As a device
A 10,000 mAh power bank
A 20,000 mAh power bank
An aluminium casing adds roughly 4 to 23 litres, depending on how the aluminium was smelted.
Per phone charge
Budget 10,000 mAh, rated around 300 cycles
Better 20,000 mAh pouch-cell, rated around 800 cycles
The smaller, cheaper one is the thirstier one. The bigger power bank takes more water to make, but it lasts far longer, so each charge costs three to four times less water.
One catch: power banks are typically replaced within two years, often long before they wear out. The lowest-water power bank is the one you keep.
Where the water goes
Most of it isn't used in the battery factory. It's upstream, in the metals.
- Cathode materials, 55%. Mostly cobalt and nickel. Cobalt mined in Congo is processed using hydropower, and water evaporating from the reservoirs is counted.
- Aluminium, 22%. The foil and cell cans. Smelting aluminium takes huge amounts of electricity, often from hydropower. An aluminium casing pushes this share much higher.
- Cell production, 13%. Making and conditioning the battery cells.
- Everything else, 10%. Graphite, copper, electrolyte, plastics.
Shares are for the battery cells, calculated from Argonne National Laboratory's battery life cycle model for a lithium-ion battery with NMC cathode chemistry.
Why cheap tends to cost more water
The studies don't compare power banks by price. They compare chemistry, cell type and lifespan, and budget models tend to lose on all three.
- Chemistry. Low-cost electronics commonly use lithium cobalt oxide cells, which contain much more cobalt than the chemistry our figures are based on. Our budget numbers are likely an underestimate.
- Cell type. Power banks built from flat pouch cells had around 66% lower production impacts per unit of energy delivered than ones built from cylindrical cells, thanks to higher energy density and longer life.
- Lifespan. Rated cycle life among 50 best-selling models ranged from about 300 to over 800 full charges.
What about lithium?
You may have seen claims that lithium takes anywhere from a few hundred to two million litres of water per kilo. The disagreement is mostly about what counts as water.
Much of the world's lithium comes from salty underground brine, pumped into ponds and left to evaporate. In the Argonne model, the lithium in the cathode adds under 3 litres per kilo of cathode material. Our reading is that evaporated brine isn't counted as freshwater there, while the headline-grabbing figures do count it. Same lithium, wildly different answers, depending on where you draw the line.
That's the problem with industrial water in general: it's rarely measured the same way twice.
How we worked it out
We counted freshwater consumed during manufacturing, from mining the raw materials to the finished power bank. That's water taken out and not returned, including evaporation. We did not count water used to charge it or to dispose of it.
| Part | Basis | 10,000 mAh | 20,000 mAh |
|---|---|---|---|
| Battery cells | About 436 L per kWh of cells, from Argonne's 752 L/kWh battery pack figure with vehicle-only parts removed | ~16 L | ~32 L |
| Circuit board | About 17 g of electronics at 102 L/kg | ~2 L | ~2 L |
| Plastic casing | Plastics at 5–7 L/kg | <1 L | <1 L |
| Aluminium casing (instead) | 80–100 g; coal-smelted to hydro-smelted aluminium | +4–23 L | +4–23 L |
What's not included
- Pollution. Water needed to dilute contaminated discharges from mining and processing (often called grey water) isn't in these numbers, so the true figure is higher.
- Brine. Evaporated lithium brine, as explained above.
- Per-charge figures assume full charge cycles and the manufacturer's rated cycle life, which real use rarely reaches.
Sources
- Dai, Kelly, Gaines & Wang (2019). Life cycle analysis of lithium-ion batteries for automotive applications. Batteries 5(2):48. Argonne National Laboratory, GREET model. doi.org/10.3390/batteries5020048
- Yang, Gu, Guo & Chen (2019). Comparative life cycle assessment of mobile power banks with lithium-ion battery and lithium-ion polymer battery. Sustainability 11(19):5148. doi.org/10.3390/su11195148
- Rieder, Louis & Elmenreich (2025). Life cycle assessment of portable charging technologies: a case study of a solar charger and a power bank. Int. J. Life Cycle Assessment 30:906–927. doi.org/10.1007/s11367-025-02453-8
Why a water company cares
Every factory in this chain uses water, and most of it leaves as wastewater. Danu Water builds adaptive electromembrane separation systems that adjust in real time to the variability of industrial water and clean industrial wastewater so factories can reuse it, instead of drawing fresh water every time.
About our water rates
Charging your phone at our table is priced in water: about an espresso's worth per charge, roughly what it takes to make the power bank behind one phone charge. Water isn't allowed in the hall, so we're happy to take a newsletter sign-up instead.
Settle up: get the newsletterFigures are estimates built from published life cycle studies and rounded. Drinking water comparison assumes 2–2.5 litres per person per day.