6-8 months ago I asked here if dehumidifier water was safe to use in tanks. The consensus was that the coils are made of copper, and the solder used to connect the coils has alot of lead, so it was not recommended.
Being the stubborn person that I am, I decided to try it anyway
My "study" was decidedly unscientific. I used the deh water to top off my 45 gallon tank 2-3 times a week. I also used deh water in my 50 gallon barrel that i over winter a tropical lily in.
Water changes in the 45 are infrequent, maybe 50% once a month. tank inhabitants are 4 comets, 2 Siamese algae eaters, and 1 bazillion snails. 8-10 varieties of plants, some copper sensitive. Results: fish grew, no diseases, I would say they thrived. plants grew, sporadic algae attacks, pretty minor. All in all, no ill effects from deh water.
The barrel has never had a water change since october, just topped off 2-3 times a week, mostly with deh water. no fish there, just a lot of snails, which thrive, 3-4 kinds of plants all doing well. no filtration at all in the barrel.
My conclusion is that at least in my case, dehumidifier water is safe for use in planted tanks. The fact that no plants that are copper sensitive died or became unhealthy says to me that the deh water contains no copper.
Disclaimer to this post!!! If you choose to try this, you do so at your own risk! I have no tests for heavy metals in water so I have only observations to go by, ZERO hard facts.