Whether for economic or ecological reasons, everyone now pays particular attention to their water and energy consumption. However, one of the appliances in the house that uses these two resources jointly is the washing machine. Conventional wisdom would say that the more clothes a drum contains, the less energy and water it consumes.

OK but The Digitals distrusts received ideas like the plague. And things being done well in the editorial office, our database contains numerous measurements of water and electricity consumption. We were therefore able to rely on it to verify whether the facts corroborate the intuition.

## Some precisions

During our multiple washing machine tests, we noted the water and electricity consumption of six different programs: classic cotton at 30°C (3 kg, then 80% of the maximum load), quick cotton at 30°C (3 kg), express cotton (3 kg), eco (80% of maximum load) and household linen at 60°C (2 kg).

Based on our study, we were able to establish that a cotton cycle at 30°C, with a load of 3 kg of laundry, requires on average 0.41 kWh to reach completion. By setting the washing machine to the same program and at the same temperature, but this time loading the drum to 80% of its capacity (still on average), we notice an electricity consumption ultimately quite similar, but higher (0.49 kWh).

Water needs are more telling. Thus, a classic cotton cycle at 30°C (3 kg) swallows 48 liters of water on average based on our tested models. And when the drum is full (80% of the recommended capacity, always), our meter indicates on average that 82 liters have been consumed.

Going by these raw numbers, the more loaded the cycle, the more water and electricity the washing machine needs to do its job and remove stains (sorry, we couldn’t resist… ). Have we faulted popular wisdom?

However, this first approach, based on unqualified observations, completely ignores an important element: the weight of the laundry. Indeed, we test washing machines of different capacities and the loads at 80% of the maximum capacity necessarily vary: 8 kg for a 10 kg model, 7.2 kg for a 9 kg, 6.4 kg for an 8 kg…

Furthermore, if the vast majority of washing machines are today capable of weighing laundry – and determining the type (cotton, synthetic, wool, etc.) – the algorithms used in the programs will not necessarily divide needs in a perfectly proportional way. Simply put, a load of 3 kg of laundry is not going to consume exactly three times less resources than one of 9 kg.

To accurately compare water and energy needs, we have chosen the kilogram of laundry as a basis. The calculation is very simple since we just need to divide the raw measurements we obtain (in liters or kilowatt hours) by the number of kilograms of the load. And in this little game, the cycles which carry large quantities of laundry are actually less greedy than their less loaded counterparts.

According to our findings, a cotton cycle with 3 kg of laundry requires on average 0.14 kWh and 16 l of water to wash 1000 g of textiles. Under the same conditions, filling the drum with up to 80% of the recommended load, a classic cotton cycle requires 0.07 kWh and 11.1 l of water per kilo of laundry. The relationships are therefore completely reversed, as these graphs show.

## Real savings for very similar performances

The savings that can be made are difficult to quantify. Washing habits are indeed very different from one household to another, and the price of water, as everyone knows, varies enormously from one municipality to another. However, you always benefit from spacing your machines and filling the drum well.

As it is quite difficult to understand what kilowatt hours and liters of water can represent, we created a small scenario based on a family owning a 9 kg washing machine (category which, according to our comparison, would be the best-selling) and using it five times a week with a load of 3 kg (i.e. 15 kg weekly).

By switching to just two machines per week and 80% capacity (the same quantity of laundry will be washed approximately, i.e. 14.4 kg), the saving on the water bill can reach €15/year in based on an average (and generally accepted) water rate of €4/m³. By performing the same arithmetic for electricity, we see that the savings are quite similar: €15 (kWh at €0.27).

In the end, we can therefore hope to save €30/year. Of course, this is a very vague scenario which does not take into account the particularities of each person, the very fluctuating prices of water or those of electricity, more stable, but which can also vary depending on the subscription, energy suppliers…

In addition, the washing job is not necessarily worse if the washing machine is full. Indeed, the algorithms often adapt the duration of the cycle to the quantity of laundry inserted. And during our various tests, we never encountered a cotton program that was much less effective when the drum was well filled or not.