Aside: I heard that "eco mode" is typically not actually the most energy efficient mode on most washing machines. Apparently it's a standard mode they have to add so that energy efficiency can be measured across machines, but that means it can't be optimised.

You're typically better off looking for some kind quick/fast mode. Or even the "regular" mode.

(YMMV, look things up for your specific model)

That's not true in the EU anyway.

Under EU Commission Regulation (EU) 2019/2023, washing machines sold in the European Union must include a mandatory standardized program called "Eco 40-60".

The whole point is to enforce strict legal limits on maximum water and electricity consumption per cycle based on the machine's rated capacity. This it the reason they tend to run for hours - it uses less water and energy than a standard cotton cycle by having longer soak times and using less electricity to heat the water.

In 1995 it took 94 litres of water and 350 kWh/a for a cycle in the average EU washing machine. These measures, amongst others, reduced that to 36 l/cycle and 96 kWh/a in 2020 and an expected 30 l/cycle by 2030.

https://energy-efficient-products.ec.europa.eu/product-list/...

https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELE...

It's one of those "optimize for X/Y/Z, pick two". The eco mode is usually the best for water usage, but it might use more energy. The fast modes might use more water but less energy. It's hard to do both and still get good results.