One of the crew members' memoir (Эдуард Овечкин "Акулы из стали") mentions that the pool was filled with freshwater. The crew rarely used the pool themselves, because they could find better use for that much water. The author had an interesting story about this swimming pool. One day, a high-ranking officer came with inspection. He was very rude and the crew didn't like him in return, especially since he sat in the captain's chair (only the captain was supposed to sit there). Then this officer wanted to take a swim and he ordered the crew to prepare a pool. As the author was drawing water, he and other crew members decided to urinate in the pool. And then watched as this officer was swimming there, barely containing the laughter. When they finally told the captain about this in control room some time later, the submarine was sailing without control for several minutes, because everyone was laughing on the floor.
Still an amazing movie.
Diagram here: https://imageio.forbes.com/specials-images/imageserve/5f40d7...
They military also spends a lot on making sure that they are very well fed - as much as they can be under the circumstances:
https://www.popularmechanics.com/military/navy-ships/a147643...
Feeding the sailors lavishly is one of their few perks.
Look at this footage. Look at the guys on the helo deck. When russian sailors have time off, they take it seriously.
The US Navy spends long hours working hard, but I promise you it plays hard when possible.
In hindsight, they catched a brief window in recent history where a western film crew would be allowed on board of a Russian ballistic missile submarine – remember that 2001 was the year when Putin gave a speech in the German parliament (in German language!) speculating about a new common safety architecture eventually succeeding NATO.
[1]: https://www.quora.com/Did-the-Typhoon-class-of-submarine-rea...