If you drop sand or gravel block onto a placed torch, it breaks into item version - that is the common knowledge. There is a range of other blocks - I don't remember them all, but rail is definitely an example - dropping sand onto which causes it to break too.
But if I water flows over a torch or a rail, it washes them off, breaking them into items.
Is there any of these items that break sand, that is immune to being washed off by water?
The falling sand breaks when the sand entity reaches a block that stops it. Then it tries to convert into a sand block. This may not be possible if there is already another block at that place - in that case the sand is dropped as item. This means the sand block breaks when it is partially inside another block when it stops falling. So all non-full height blocks will break sand e.g. torches, slabs, pressure plates, enchanting table etc.
Water will break all plants except reeds and cactus and all circuitry blocks + a few others: button, end rod, flower pot, lever, rails, redstone dust, repeaters and comparators, skulls, torches, string, web, and trip wire hook.
Here is an exhaustive list of blocks that fit both criteria:
