Okroshka should be prepared with kvass - this is fixed in the new GOST for Russian cuisine.
Rosstandart approved the document, it is called "Traditional Russian cuisine. Recommendations for cooking technology".
The new GOST contains recommendations for making 132 traditional dishes, including borscht, pancakes, dumplings, Olivier salad and herring under a fur coat.
GOST is voluntary; Restaurants can prepare dishes according to their recipes.