No dialog and/or sound, makes it even more difficult to identify. I wouldn't bother trying to find it myself.
There have been a great many films, mostly during the 70s-80s, that I remember seeing and enjoying but I do not know any names of the people, or titles, or year or the studios info.
When its a European film, then its even harder/impossible to identify.
However, with some studios, they have a recognisable style that can be instantly identified. For example, Mario Salieri films all have the same "look and feel" / atmosphere, so you can identify them as soon as the film starts, even if you don't know the title. Not all studios are as easy to identify as Mario’s stuff, but you might be able to narrow the possible studios down to a few, rather than lots.
Your best bet is what I mentioned before, which is to search with various combinations of relevant keywords.
If you want to put in some work to identify this film, then you can also look at these elements to look out for.
• Furniture - if any, when do you think that style was around?
• Clothing - 70s clothing is easy to identify, as in 80s clothing.
• Hairstyles - 70s hair styles are easy to identify. 80s hairstyles are also identifiable, like permed hair and "big hair". You can search the evil G for 70s or 80s hairstyles if you don't know about hairstyles, so you can have an idea.
• Accessories - In the 80s, many people wore big glasses, so this is another thing that might help you.
• Mannerisms - The way people get into sex has changed over time. 70s scenes often had people fully clothed and laying down on the bed or sofa and then clothing would come off slowly. Kissing was more common in the 70s.
• Cunt hair - it was rare to see shaved cunts or it may never have been seen during the 70s and 80s.
• Public scenes - if there are any scenes of streets, public buildings, etc., and the type of cars they show can tell you roughly which decade the film was shot in, as can any advertising on boards, buses, taxis, etc., and any scenes showing famous brand names that no longer exist (like Pan Am), etc.
If there are public scenes showing shop fronts, then the language of the shop names will tell you which country the film was made in.
Maybe none of the above are helpful to you, if all you have are random people fucking in a shower area and there is nothing noteworthy about the setting or the people. Coloured shower tiles tell me that its most likely to be from the 1970s-1980s and maybe early 1990s.
In the 70s and 80s, there were lots of compilations of short clips put together called Loops, often featuring no name performers who never did anything else after.
These Loops might be your best chance at finding your film. Some Loops to look for are;
Color Climax
Rodox
Swedish Erotica
Ribu
There are websites dedicated to vintage porn, but they all require a title to be entered for results or are title centred. Some of them can search by a name too.
Its going to be a lot of work.