What's the difference between the red, the yellow, and blue hydrants?

The location of the Fire Department.

The different colors indicate the water flow the hydrant will provide (useful info for fire fighters).

Visibility. In my county they are all silver with reflective metallic paint.

Other jurisdictions use other paint schemes for visibility. (In my county, they put a blue reflective plastic thing in the road so the fire department can easily locate the hydrant.)

The color refers to the Gallons Per Minute, GPM, of available flow.

Source :
“In an effort to make it easier for firefighters to know what a specific hydrant will supply, the National Fire Protection Agency (NFPA) recommends that fire departments and water districts follow a set standard of color-coding. Known as NFPA 291, it says fire hydrants using public water supply systems should be painted chrome yellow, and their tops and caps should indicate the available GPM. Below 500GPM should be red, 500–999 GPM should be orange, 1000–1499 GPM should be green, and 1500 GPM or more should be blue.

It varies regionally. In Montreal, blue hydrants are for the metro system, so you can park in front of them without getting a ticket. And the red hydrants with these crazy attachments are drinking fountains as well as hydrants. I don’t think I’ve ever seen a yellow one here.

^^ what’s that? Turning wheel may be?

I think ours are all red. I wonder if they’re all below 500GPM.

In 1976 people went nuts painting them red, white and blue. Everything was red, white, and blue that year

@imrainmaker It’s a way of raising the height of the water so that people can drink it without crouching to hydrant-level. It was designed by an industrial design group in Quebec (linked page is in French).

I forgot about the white ones. I never saw orange or green.

Thanks @LuckyGuy and @dappled_leaves (best 2 answers) and @Lightlyseared and @elbanditoroso and @Call_Me_Jay.and