Yes that's what we also do at home, we used the "rinse water" from the washing machine and we use them on the plants and trees. But we only use the ones that are diluted the most of soap, so we wait until the final rinse to collect the water being drained from the washing machine rather than using all the drained water from there, since the early batch of water would be still soapy.
You can never go wrong with reusing water but when it comes to watering plants, other considerations emerge. For instance, its not sensible to use laundry water to water fruit trees as this is likely to result in contamination. Its best suited to ornamental trees and fences to reduce water bills as cleaner water can be used for other purposes.
We rotate the water from the kitchen and bathroom to the garden. And then the water given ends up watering most of the plants. Also the end of the water pipe from kitchen and bathroom then helps with the soil nearby. So it all works out in that way. I think most of us can definitely do something like that in that case.
My father used to do something similar to water the rosebushes and the garden. We used to have a dehumidifier in the basement before we got air conditioning so he would use that water to water the plants. It saved using water from the faucet and it saved money doing this. This would help also when there was a restriction put on water use from there being a drought.
I think a rain barrel might be a easier way to save water for your garden or your trees because rain water is more of a soft water-meaning it lacks minerals or chemicals that ground water or municipal waste has in it. This water has lots of nitrogen from the sky when it falls and these rain barrels are usually quite cheap-although you might want to be careful about the roofing material that it runs off of though ?
Used water that contains things like soap or washing detergents is not good for trees. There is a tree at my place which used to produce avocados but not anymore. The tree dried and there were no leaves. This is because of soapy water. When people washed clothes and disposed water on a small river which was created to act as a drainage system, all that would be absorbed by the tree since most of that water was flowing towards and beside that tree.
Soapy water can only be used in an emergency situation, when there is no fresh water at all. If it has to be used, it should be highly diluted.Most soaps and detergents contain chemicals that can be harmful to the cells of plants. Using soapy water to irrigate plants can easily make the plants to dry up. It has the same effect as using hot water to water the plants.
