Hey
Yes you can use tap water of course if it is clean and drinkable(in my country it isn't)
If you don't close it 2 things will happen your freezer will be contaminated with naphtha and water will condense inside the jar causing some problems when drying the dmt..
Freebase DMT is not soluble in a solution of sodium carbonate and impurities like if you pulled some lye and plant material(sometimes undetectable with eye) are soluble, so when u wash with SC these impurities are washed away and the dmt is more pure..
Hope this was helpful
Good luck on your extraction
"Is this the end of our adventure? Nothing has an end. We came in search of the secret of immortality, to be like gods, and here we are... mortals, more human than ever. If we have not obtained immortality, at least we have obtained reality. We began in a fairytale and we came to life! But is this life reality? We are images, dreams, photographs. We must not stay here! Prisoners! We shall break the illusion. This is Maya. Goodbye to the holy mountain. Real life awaits us." ~ Alejandro Jodorowsky