How do I make a variable that every second it will add a number to it (timer)

make a global variable of type number and scope player_lifetime:

then inside your tool's triggers add a new toolinhandtick and make this procedure:

i didn't make it reset each time you hold another item, but you can do that yourself just by making a new global procedure that changes watereffect for each tick depending if you're in water or holding an specific item