Some washing machines in Japan come with a long hose that can be placed into the bathtub to pump out leftover bathwater. If you have never seen this before, you might wonder, “Do people really wash their clothes with water someone has already bathed in?”
The main purpose is simple: to reuse bathwater, reduce the amount of fresh tap water used for laundry, and save money on the water bill.
A Japanese bathtub can hold a large amount of water. Instead of draining all of it away the next morning, some households reuse part of it for laundry. That means less fresh water has to be drawn from the tap.
There is also an important difference in how baths are normally used in Japan. People generally wash their bodies before getting into the tub. The bathtub is mainly a place to soak and warm up after washing, rather than the place where dirt is scrubbed off the body. Because of this, using leftover bathwater for the washing stage of laundry does not necessarily seem especially strange.
Of course, the water has still been used for bathing, so it is not treated exactly like fresh water.
The hose makes reuse much easier. Its end is placed in the bathtub, and the pump draws the water directly into the washing machine. Without the pump, carrying that much water by bucket would be impractical.
Exactly how the bathwater can be used depends on the machine. Some models use it only for the main wash, while others can also use it for an early rinse. The important point is that the feature is not designed to make every stage of the laundry cycle run entirely on leftover bathwater. Many machines allow the final rinse to be done with fresh tap water.
This makes it possible to reduce water use while still finishing the laundry with fresh water.
Not every household uses the feature. Some people find putting away and cleaning the hose inconvenient, while others simply prefer not to reuse bathwater for hygiene reasons. The pump and its filter also need regular cleaning.
So the bathwater pump is not there because Japanese people think used bathwater is the same as clean tap water. It is a practical way to reuse a large amount of water that would otherwise be drained away, cutting tap-water use and helping reduce the household water bill. The washing machine simply makes that reuse much easier than carrying the water by hand.
References
Hitachi, “How to Use Bathwater for Washing (Oyutori)”
Sharp, “How to Use the Bathwater Pump”
Sharp Washing Machine Instruction Manual, “Using Bathwater”
Sharp, “Cleaning the Bathwater Pump”
