I just think the novelty of these type of displays was up in the 90s, It’s time for an upgrayedd. I propose leprechauns flying up and down the river wearing water jet packs, shooting people with their Chicago-style hot dog cannons would be more with the times. What’s your idea?
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There are water-tracing dyes out there that are designed specifically to be able to dump into water to see where it’s going – like, to find leaks and such – and I bet that they’re using one of those.
IIRC you can normally get red or green.
googles
https://www.amazon.com/water-tracing-dye/s?k=water+tracing+dye
LPT: if you need this for home purposes, for example to find where your toilet tank is leaking, kool-aid works really well.