There is also the possibility of mixing a small amount of bleach or detergent in the water, but both of those solutions could cause problems. However, who knows.... soap scum buildup..if it is an organic/beautiful? soap, could cause a really interesting texture or transparent layer on the paper. Could be neat. If a waxy soap, then the layer accumulated could also serve in preserving the paper and plant after watering has stopped. Lots of stuff to test! Good luck and thanks,
Katie Smither