YOU ASKED: Is it reliable to use rainwater? What are the consequences (pros and cons) of doing that for a dyebath? What should I be aware of (more acidity perhaps?)?
KATHY ANSWERED:
Rainwater is usually softer and more acidic than groundwater, so you could see a difference between colors dyed with well or groundwater and those dyed in rainwater. Some dyes such as cochineal and lac benefit from softer or demineralized water and rain water could be useful in that situation. I used to struggle to achieve bright cochineal pink shades when I lived in an area where our water was highly mineralized groundwater. I resorted to mixing rainwater 50/50 with hard tap water and achieved much better results. However, many of the classic dyes such as madder, weld, logwood and many of the yellow dyes love mineralized or hard water, too. Indigo does not seem to be affected by rainwater or groundwater, so you probably don’t need to worry about the water source for indigo vats. Capturing and storing rainwater means that you should be aware of mosquito larvae and algae happily living in your rainwater tank unless you have some way of keeping them out. Also be aware that rain barrels that are attached to roofs can carry a lot of debris, bacteria and metal residue from the roofing material into the rain barrel. It’s probably best to let the first few storms “flush” the excess debris from the roof before you start collecting and storing rainwater.