Answer: Unfortunately I am not certain I am exactly clear on the set-up you have in mind, however you could line the basin with plastic and use a sheet of clear plexiglass or acrylic behind the running fountain or any splashing water to protect the mosaic on the wall. (You might end up with a problem with algae on the grout and water stains on the tile.) Alternatively, there are many clear sealants available and perhaps one of them would do. Keep in mind that terra cotta and brick are somewhat porous unless fired to a high temperature, so this is why I am suggesting lining it in some way. The liner would also make the occasional cleaning easier.
Tropical water lilies, papyrus, water lotus, water hyacinth and other tropicals would all love the heat. What a lovely project for your conservatory!
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