Of course bathrooms have many features, such as lighting, flooring, windows, and wall coverings. These often are subject to personal tastes and requirements, although there are many universal design guidelines that can be followed in selecting them. Still, none of these are part of the essential three.
There are many necessary features in every bathroom also. These include the tub or shower, toilet, and sink. While these are three in number, they aren't the essential three referred to in this post.
Other items that can be found in many bathrooms include a counter, faucet, mirror, vanity or cabinet, accessories such as towel bars or rings, and even a linen closet. These aren't part of the essential three either.
The first item of the essential three that needs to be in every bathroom is a safety grab or assist bar installed vertically (at a comfortable and accessible height) just outside the entrance to the tub or shower - typically at the back, but whichever end in usually entered and used for exiting.
Everyone has, at sometime in their life, needed to grab onto or hold something for additional support as they were getting in or out of the tub or shower. They may have felt dizzy, they may have had a sinus or ear infection that affected their balance, they might have had a leg or ankle injury (a sprain, for instance), they could have had stitches in their leg or foot from an injury or surgery, they might have had a severe cold or the flu that made them weak, they could have slipped or misstepped getting in or out, or they just might like the security of something to hold onto.
The second essential item is related to the first. It is a seat of some type - either a folding seat that can be deployed for use and then returned to its closed position, or a built in seat or bench. For reasons similar to those for having a grab or assist bar to hold onto, the seat gives people a place to sit safely when they are fatigued, dizzy, unable to stand for a sustained period of time, or have a foot or leg injury, muscle pull or cramp, or just want to rest for a moment or have a water massage.
The third item is a handheld or personal shower - and make sure it has an on-off control or switch on the wand. These used to be installed infrequently but now are very much in demand. They have many uses, including bathing or rinsing (while seated on the bench or seat), washing or rinsing one's hair, keeping part of the body from getting wet during an injury or post-surgery, assisting a child to bath, washing a dog, helping an adult that can't bath alone, or rinsing down the walls and floor of the shower or tub after each use.
There are additional reasons for having each of these three essential items included in any bathroom, so let's make a point of recommending and installing them at every opportunity - regardless of the physical needs of our clients. Everyone can benefit from having them.