Looking for a cheap water meter for a faucet

Hey all! Using a filter for my living organic soil cannabis grow and I was recommended by the guys at Black Swallow to get a "water meter" for it so you can track it's lifetime ..

This is the filter https://www.amazon.ca/52700-Inline-Flex ... B01N8TYQ9W

And I guess I'm looking for something like this? https://www.homedepot.ca/product/rainwa ... 1000743354

But it says unavailable in my area. Found a couple obscure ones out there but they're priced pretty steep. Maybe I'm searching for the wrong item, or wrong terms?

Much appreciated in advance folks!

CHEERS