It depends on the rules and laws of your local government as to whether gray water is allowed to be used.
Check with your local government about the use of "gray water." You would only use the rinse water, not that with soap.
Most laundry detergents work just as well with cold water. By using cold water you will save money and reduce environmental damage. It depends.If you are putting laundry in the washer then use hot water.If you are washing laundry that stains its colour or just washing by hand then use cold water.
Water will thin out laundry softener.
You don't use it in your bath water.
In wad=shing laundry, you use aproximittly 592.8 gallons of water each minute.
yes, I use it all the time and it is just fine
Laundry
Depends on the plant. But things like crabgrass and weeds can grow in abundant sources of water with just about anything short of poison in it. It's no the fact that the water is dirty or has laundry soap in it, it's the fact that the water source is abundant and regular. A more sensitive plant might be killed by laundry detergent. If you want to use compost as fertilizer i.e. those dirty underwear, go right ahead!
Too many variables to give a good answer. By hand? How much laundry? Front load machine? etc.
10 to 20 litres a day
You may have a small hot water heater in your house or apartment, this will use up all the hot water in doing laundry so the tank needs to fill up and heat again.
55% of americans use tide laundry detergent over other regular laundry detergents.