Char all the vegetables. Keep the garlic skin on to avoid burning it. Use a frying pan to char them. No need to add oil or anything. Just put the tomatoes, onion and garlic on the hot frying pan and char them until blacken. Peel the garlic before adding it to the blender.
For this salsa I didn’t toast my arbol chillies, but if you want you can do it. Just do it quickly, maybe one minute.
Add everything in a blender, add salt and cider vinegar and blend until smooth. Add the water to make it runnier.