In modern times, the UK was the first country to make use of walk-in baths; in the UK, they have been available for forty plus years.
From the UK, the use of walk-in baths spread to Canada, and then eventually to the US. Today there are hundreds of vendors in the US and in the UK selling a wide range of types and qualities.
The biggest leap forward in the design of walk-in baths has been the outward opening door. For decades, virtually all walk-in baths had inward opening doors due to the problem of leaking. The disadvantage of the inward door is that the user has to squeeze into the corner of the bath to allow the door to swing shut. This limited their use to those only with moderate mobility issues and limited their use for the long-term.
About five years agowe saw the design of an outward opening non-leak door come to fruition. The problem was solved by having steel pins coming out of the door edge into the door frame resulting in no leaks, plus the evolvement of medical grade silicon "rubber" seals instead of the old black vulcanised rubber that perished.
Significantly, this meant walk-in baths were suitable for a much wider range of disabilities and catered for advancing impairment.
Most walk-in baths today have outward opening doors, they are wheelchair friendly and also allow space under the bath for use with lifters such as the Arjo maxi-lifters.