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A toilet shelf
The wall behind the toilet is often unused space so it's the perfect place to put a shelf or a cupboard. This should help with the storage space problem.
Sliding doors
A door that opens into the room will deprive you of some floor space because you have to have room to open the door fully. Using a sliding door can solve this problem. Doors can slide against the wall or better still, inside a cavity wall, which will recover all the space lost to the door opening.
I was unable to use this approach in my small bathroom remodeling because I didn't have a suitable wall but I did look into it.
Curved quadrant shower enclosures
In any small bathroom design shower arrangements must be thought about very carefully. If you are including a shower cubicle then consider a curved quadrant design. These cubicles are flat on 2 sides with a curve to complete the enclosure. They save a lot of useful space in the rest of the bathroom because they eliminate the fourth corner of the enclosure, which often gets in the way. A curved quadrant shower cubicle worked well in my small bathroom design.
Use the door for hanging towels or robes
If you still have a conventional door in your new small bathroom design then make the most of it by putting a towel rail or a robe hook or both on it. This could save you wall space elsewhere.
Lift the radiator off the floor
Radiators are often found taking up floor space when they don't need to. Move it to a higher position. I moved mine over the end of the bathtub, which was a good compromise.
Combine the radiator with a heated towel rail
If you choose the right type of radiator then you can also use it as a towel rail. Not only will you save space by eliminating the rail, you will also get lovely warm towels to use.
Shower screens that fold away
If you have no other alternative than to shower in the bath then you might want to use a shower screen rather than a shower curtain. If you do, look for a shower screen that folds away when it's not in use.