I've used rainwater in the tanks since the 1970s.I've run planted tanks using 100% rainwater very successfully in the past
It will be fine for soaking the wood, if you use it for water changes you would need a conductivity meter to tell you whether it is salt contaminated.I’m also by the sea so I’m not sure if that should be considered?
I just collect it from the house roof, I've got three butts in the back garden (below) and <"two in the front">.Are you all storing rainwater in water butt from guttering from house/garage or special set up??