Place the yogurt and water in a large pot and bring to a gentle boil while stirring. Reduce heat and simmer uncovered over medium heat for 2.5 hours, stirring occasionally. During the final 1/2 hour you do need to stay with the pot and stir frequently and adjust the heat as needed so that the yogurt curds aren't burning on the bottom.
You should have a pulpy, aromatic and slightly darkened curd in the pot at this time.
Once the curds have cooled off a bit, place them in a cheesecloth and attempt to wring out as much of the liquid as possible. The liquid is typically discarded, however, if you are feeling adventurous save the small amount of liquid and incorporate it into soups!
Place the pulp in the blender, add salt and water and blend for a minute or so on high speed. Homemade Kashk will always have a grainy feel to them, so blending them longer can reduce the graininess.
Once pureed, taste and adjust for salt and consistency. It should definitely be salty but not overwhelmingly so and it should feel like a thick sauce.
Fresh Kashk will last in the fridge for a week or so, otherwise plan on freezing them in small batches for future use.