Indeed, the Russian fasting school (Sergey Filonov, Igor Khoroshilov, and others) prescribes undertaking 1-3 days of dry fasting before water fasting, not vice versa. Logic is as following. They proceed from the idea that the main healing effect of water fasting starts after 5-6 days from the beginning, after the so-called acidotic crisis (see https://dryfasting.info/duration-of-fasting/ ). Dry fasting accelerates the onset of the acidotic crisis. In this case, it occurs on the second or third day, not on 5-6th day. So if you undertake a dry fast before the water fasts you get in the healing period a lot faster. When you are in, you can switch to water fast.
Note: correct name is Filonov, not Filinov.
You can dryfast and waterfast and alternate between the two. It depends entirely on you. The question that was asked of Dr.Filinov is can you go from a 40 day waterfast into a dryfast his recommendation was “no” because it would be too taxing on the body. This is probably true for most people. But, again it depends entirely on the person. Because some people can fast for 40 days and still have an abundant of fat on there bodies and feel no intense fasting effects. In this case switching to a dryfast even after longer than 40 days would be completely okay.