In Sweden, almost all of my electrical bill is heating anyway and water is practically free.
My dishwasher's default program requires 4—5 hours. In the 90s, this was <1h I think?
https://www.youtube.com/watch?v=_rBO8neWw04
TLDwatch: eco programs use only one batch of water, others use two and that results in cleaner dishes with the added benefit of a faster program.
I feel like I read that in the manual that comes with my dishwasher. It was worded a bit differently, but it essentially said to use auto mode to get cleaner dishes, not eco which saves money but doesn't clean as well.
The same is true for energy efficient washing machines by the way, they often do not reach the temperature a program states and compensate with longer washing times. This may be problematic for hygienic reasons at times but has a noticeable impact on energy use.
> It's not as if the dishwasher hoards very much water for a load.
Apologies if I misread this but dishwashers absolutely _do_ hoard and reuse water. My dishwasher claims to use about 12l of water for a full wash, which really isn't much at all.
And also that using already-hot water gets it closer to the desired temperature at least, meaning less work for the heating element. If you're using a conventional water heater that's just pointlessly keeping your water hot all day, I figure you might as well use it. But of course, there's still a net loss of hot water that must be replaced using energy, so at best.... (you know what's coming)...
It's a wash.
https://www.sgu.se/grundvatten/grundvattennivaer/aktuella-gr...
The water savings with eco-programs compared to "normal" programs is in the range of 10 seconds to 1 minute worth of shower time, if I remember correctly. If you want to conserve water use, there are a lot better ways to do so than running a dishwasher in eco mode. (Washing dishes by hand uses more water on average than even an old dishwasher).
Then, the terminology of "waste" is a bit problematic I think. The dishwater will usually output the spent water into some kind of sewer system in most places, and at some point this water usually gets cleaned and put back into circulation pretty much straight away. If not, it usually reaches nature again eventually. It's not like it became so toxic it needs to be stored safely for millennia.
That doesn't mean we shouldn't be mindful, of course, especially when there are current (regional) shortages.
Energy consumption (mainly to heat water) is a different matter. Energy consumption is the real environmental cost, not water consumption, as water is basically renewable, but energy is often produced from non-renewable sources and has secondary effects such as carbon emissions, which in turn effect climate change and in turn regional water availability. But even then again, reducing shower time by a minute, or water temperature, will have a greater impact on energy consumption than running a dishwasher in eco mode (on average).