change item to another item when touch water

This worked for me: 
 

It also helped me a lot! but I would like to know how do I add more items when thrown in water? I tried to add an "and" to the convert item entity but it didn't work. I wanted to play a diamond + redstone and get another item, can you help me?

To detect if two items are together, use else if and convert, in which you put the second item. Then, in each item choice put IF -Exists Square cube 1 of X of entity iterator Y of entity iterator Z of entity iterator subtype of item, if convert entity iterator to (other item) despawn entity iterator, despawn nearest entity in square cube 1 X of entity iterator, Y of entity iterator, Z of entity iterator of subtype item

Can you send me an image of how to assemble this procedure? I have a little trouble.
Thanks in advance for your help.

actually, that didn't work. I put this together and it does though. 

I made a bit of a mistake, the last itemhere variable needs to be set to false.

Thank you so much!! 

Is there any way to do this, but with a block that isn't water? In other words, could I throw my two or more items onto a certain block of mine that isn't water, then get one item as an output? Thank you!

Please, can anyone help me?
I would like to do this same process in a cauldron, instead of pouring it into a potion of water.
I would like the player to throw some items into the cauldron and then it would turn into a single item.