DMT has a pKa of 8.68. At pH 8.68 50% is ionized. At pH 7.68 90% is ionized. At pH 6.68 99% is ionized. The ionized form is water soluble. The unionized form is practically insoluble in water. So you want the ionized form.

Absolutely pure water has a pH of 7 until it sits around for a while and then the pH drops to about 6 or so. But some tap water is hard water and can have a pH higher than 8.5 and would be poor for extracting DMT if it was too hard. If you have hard water, you might need to bring the pH to 6 for best results by adding some sort of acid. Actually though, the plant material itself has a pH of about 5-6 anyway, so normally, even if the water is hard, the plant material will bring the pH down to 6 or less.

Some forms of DMT are more water soluble than others, so picking the right acid makes a difference. The DMT in mimosa is likely DMT tannate. Little is known about DMT tannate’s water solubility. Natives never add acid to their brews and their brews work just fine. You don’t want something like DMT fumarate because it has poor water solubility. DMT acetate has great water solubility and is made by simply adding vinegar.