Plumbing Question

[Chelsey Martin]

Hello! So my fiance and I are tenants in a lovely older home. Only problem is our bathroom water pressure is horrid. We called the landlord about it and they told us there is nothing they can do about the water pressure. 

So my question  is: can we call a plumber and have them look around to find the problem without asking for the landlord's permission? We also have yellow rusty water and because it's an older house we're worried the pipes are all rusty and bad and just want things checked out by a third party professional. Then we want to take that information to the landlord and have repairs done. 

We're also fine paying for the plumber and repairs ourselves if the landlord deems it unnecessary to fix. We just want our water pressure good and the water clean for ourselves. 

If it helps we live in Wisconsin.