Cut the large tomatoes into quarters and add to a blender along with the onion, garlic, basil, cilantro, parsley, vinegar, and salt. Puree the mixture for several minutes until it reaches the consistency of a smoothie.
Set a fine-mesh strainer over a medium bowl and line it with a piece of cheesecloth. Sieve the mixture through the strainer, using a spatula to press it until all of the liquid is extracted.
Pour the tomato water into a mason jar or freezer-safe container. Store it in the refrigerator for up to 2 days—shake before using—or freeze for up to 3 months.