I've been building a bathhouse in my fortress so my dwarves can clean themselves without leaving the fortress, train their swimming and get happy thoughts from mist. I decided to use an aquifer as both the source and the sink for my bathhouse drawing water from it and draining into it. Since I am not an expert dwarven plumber I decided it would safer to build the bathhouse above the aquifer to avoid flooding the entire fortress.
The one issue with this is that the layers above the aquifer are almost entirely clay meaning that I need to resurface everything to avoid turning my bathhouse into a mud pit. So I went ahead and covered every surface with marble blocks. However much to my dismay when I opened the floodgates to allow all the water to fill my baths everything filled up with mud. So had the cleaners rip up all the floors and lay down new floors (since that seems to be the only way to get rid of mud (I guess mud stains marble?)) filled in a couple of gaps that I thought might have been the culprits and ran in again. And again it just coated the entire room with mud.
At this point I am noticing that my grates, pressure plates and floodgates remove the floor beneath them when constructed. And I am wondering if this is the source of the mud. Would this be a place where mud could contaminate my water? Is there something I can do to prevent this?
Here is the layout of my bathhouse for reference, all the constructs pictured are made of marble blocks if it matters:
Lower level:
▼
╔X╗
╦╦═══════╝╫║
╬╣▲+++++++^║
╬╣▲++++++++║
╬╣▲++++++++║
╬╣▲++++++++║
╬╣▲++++++++║
╬╣▲++++++++║
╬╣▲++++++++║
╬╣▲++++++++║
╬╣▲++++++++║
╬╬╦╦╦╦╦╦╦╗╫║
╬╬╬╬╬╬╬╬╬╣^║
╬╬╩╩╩╩╩╩╩╝╫║
╬╣▲++++++++║
╬╣▲++++++++║
╬╣▲++++++++║
╬╣▲++++++++║
╬╣▲++++++++║
╬╣▲++++++++║
╬╣▲++++++++║
╬╣▲++++++++║
╬╣▲+++++++^║
╩╩═══════╗╫║
╚X╝
▼
Upper Level:
═┼▒▒▒▒▒▒▒▒▒▒
++▼ ▒
++▼ ▒
++▼ ▒
++▼ ▒
++▼ ▒
++▼ ▒
++▼ ▒
++▼ ▒
++▼ ▒
++++++++++#╚╦O
++++++++++#+X÷÷▼
++++++++++#╔╩O
++▼ ▒
++▼ ▒
++▼ ▒
++▼ ▒
++▼ ▒
++▼ ▒
++▼ ▒
++▼ ▒
++▼ ▒
▒▒▒▒▒▒▒▒▒▒▒▒
(I've used the ANSII symbols from the game for these diagrams, if you have a question about a specific symbol I can tell you what it is, if you are unclear of what this diagram depicts at all I can add a legend, either way just leave a comment.)
Best Answer
In Dwarf Fortress, mud is not created when water touches soil. Instead, it is created when water touches any surface. No matter what the flooring of your bathhouse is made of, some mud will always appear once you open the floodgates.
On the bright side, mud doesn't really matter as long as you're not trying to drink the water, so I wouldn't worry about it.