Mineral water has the Spanish in the street at zero ... nothing less (7)

'mineral water' is the definition.
(seltzer is a kind of mineral water)

'in the street at zero nothing less' is the wordplay.
'in the' indicates putting letters inside.
'street' becomes 'st' (abbreviation).
'at' becomes 'el' (I can't justify this - if you can you should believe this answer much more).
'nothing' becomes 'O' (looks like zero - 0).
'less' suggests deleting specific letters (less can mean minus).
'zero' with 'o' removed is 'zer'.
'st' going around 'el' is 'selt'.
'selt'+'zer'='SELTZER'

'has the spanish' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.

Can you help me to learn more?