I did try using the dehumidifier water over the colder months when the dehumidifier was on most evenings. It worked well, this is what I did:
1. Wet hair with warmed dehumidifier water
2. Add baking soda to a little water to make a paste and rub into hair
3. Rinse with more warmed water
4a. Rinse hair with camomile tea made with dehumidifier water (optional)
4b. Rinse hair with diluted kombucha vinegar (or
apple cider/scrap vinegar depending on what I had).
Over the summer months, I had to go back to using tap water and a septic tank safe shampoo. I only have to wash my mid-back length hair every week now so it's a lot less shampoo than before. I will use the dehumidifier water again in the winter.