>I also don't want to put your idea down, but there are planes dedicated to each element in the astral, inhabited by the elementals, at least from what my friend told me and from what I've gathered from studying Hermetics and other Western magics. So you say that the "astral water" would be the astral proper, but then again you have earth, and fire and air in your "astral water" then.
The elements can be used to categorize anything and everyhing, all we do is divide things created by the elements into elements so we can understand the products of the elements through the elements. Sup dawg, I heard you liked elements…
In such a way, it's perfectly acceptable to divide the water element even in it's purest form into four elements to understand what constitutes it. To understand how it arises (fire), how it operates (air), how life emerges from it (water) and how it can manifest (earth) and many other things analogous to these elements.
While elements are real powers that have real effects in the mental, astral and physical planes, they opperate in accordance with their laws too, so in a sense, they are also principles which govern each manifestation and since all things manifestedd have been done so by the powers of the elements, the elements themselves opperate through the elemental principles. So all things that exist, still have within them four elements, otherwise, it would simply not exist, the elements always function together at all times.
This means that manifestations categorized as "watery" or operating in regards to the water element, only means that the dominant elments within it is water, it doesn't exclude the other four, otherwise, it wouldn't be a thing in the first place.
And as for the whole etheric and astral, these distinctions are just words, the differences between "etheric projections" and "astral projections" depend on their level of manifestation. which isn't that far of a thing.
Taoism has a very very useful classification of the various types of astral body manifestation. From all the schools, I'd say taoism best describes matters of transmuting the body through energy and attainments of various powers as a result from cultivating the astral/energy body and physical body as their whole way of cultivation is to purify and transmute their energy bodies and become a taoist immortal through mastery of their astral/energy body.
As such, they classify various stages of "astral projection".
The Yin Shen body and the Yang Shen body. And within these two categories there are various levels of attainment. Most if not all of what the western terms "astral projection", "OBE's", "etheric projection" and "soul travel" belong to the Yin Shen body type of projections.
The distinction lies in that the yin shen body is an energy body that is latent and naturally occurs, making achievements related to it much easier then it's counter part, the yang shen body. This yang shen body, can only arise when all of the elements of the astral/energy body have been transmuted. That means, there can be no yang shen projection if one hasn't transmuted his jing to qi and his qi to shen (in yogic terms that would be one who has been successful in the practice of pranayama and has observed bramachaya), awoken the prenatal qi (kundalini) of the body AND cultivated/trained the yang shen body (which comes with it's whole set of instructions, neat things and pitfalls). While the Yin shen body is natural and latent in all, the yang shen body types of projections only arise when you have rigorously andthoroughly cultivated them.
The yin shen body is totally immaterial, even though it may limitedly interact with the physical and even lead to apparent telekinesis in it's higher form. The body from which the projection is made, the physical body is put into a yin consciousness of sleep, it breathes, needs to eat, is awoken easily and can be also distracted easily,… While the yang shen body can be made material, or immaterial at the discretion of it's user and when projected, the physical body is put into a yang state of samadhi. This means that one who has attained the yang shen body can not only manifest physically during his wanderings, but his body is put into a deep state of samadhi, thus his physical body will not breathe, and he will look like he is dead to the outer world, however, his body will never deteriorate and even if he comes back centuries later, he will find his body just as he has left it. Thereby achieving taoist immortality.
All of this is just to show that there is a WHOLE LOT of complexity and things to achieve in these matters and also that all schools talk of the same things with various levels of depth to the subjects. Yoga doesn't really give methods of astral projection, as through the success in it's practice, it is extremely easy for the students to develop these abbilities to the same level as taoist immortals themselves. There are many reporst of yogis talking about these achievements and the worlds they have visited, the bilocation phenomenon they have brought upon,… Some other schools don't talk of many other things either and yet are still extremely valid and much more detailed in other regards. Zen doesn't talk of energy cultivation but through it's methods, it becomes extremely easy for the student to cultivate properly and intuitively by himself. All schools aim to create self sufficient spiritual individuals. Yet, the saints and the buddhas of all schools have a path of their own to still walk on, there is no end either.
All in all, while both the etheric body and the astral body and the pranic body are the same, depending on the context, they talk of deeper and more profound atainment. Same goes for the relationship between the tattwas, the elements, the taoist 5 elements that include wood and metal (dafuk?), the skhandas,…
They all talk of the same things, but in a different context, and adress themselves to people with different levels of achievement in specific matters. The 5 taoist elements make a LOT of sense when used to diagnose physical issues. They get a bit awkward when it's time to talk of astral or mental matters, the skhandas are amaizing for the mental, a bit more awkward on the physical, the tattwas do an awesome job describing astral things, while they fall short of the subtler mental issues. Yet, they are the same subject, and they all are solving a problem in different ways, which is why sometimes, the correspondances can get a tidbit hazy. When discussing different sytems, It's always importat to know what the system was made for, who it was made for and what level of achievement is talked here, in addition to the planes it is talking of and the powers at use.