How do i use it. Everytime I try it wont enter the tender's water tanks (Scotsman) and I cant turn it on
I'm not sure the water tower was ever made to work. It's likely just for decoration as the route was made long before steam locos were in TSW. I could be wrong though.
It's not dumb, it's just the way the game works. The same with aggregates, you can drive your train under the hopper as much as you like, nothing will come out of it because there no instruction on your service to use it. There's a scenario on peak forest where you stop and fill up with water if you want to have a go at doing it.
The water tower should work in free roam, are you doing these steps? Turn the water pipe arm until it is over the track Open the water tank lid Pick up the end of the water hose Climb up the back of the tender and move the hose over the water tank The hose should attach itself (though there will be a gap, since DTG didn't put the coordinates in the right place) Turn the water valve on