A question we get asked over and over, is how does one dilute liquid natural latex if it becomes too thick. Of course, thick is a relative term, so it's more about flow control when brushing, or air brushing liquid natural latex.
Tap water should not be used, as it may contain Calcium (Ca) and Magnesium (Mg) salts. Even small amounts of these salts have a tendency to coagulate natural latex.
If you find that you must thin out your liquid latex, then you should simply use distilled water.