Here's what my engineer friend had to say about it....
" We didn't make
HDPE parts, but I can offer an opinion.
The gas can is most certainly HDPE, the same as the water jug, and
many food containers at the store. The only concerns I might have
would be whether the red dye is safe, and whether any coating was
applied to the inside of the gas can.
I wasn't sure about the food grade question, so I did a little
looking. There are FDA-approved "Food Grade" plastics, and this
approval is based on purity and what types of dyes are used.
That being said, I wouldn't worry about it. Once it's been washed
out, I doubt it's a problem. Especially since the water isn't in
there for very long. I would drink the water."