Rust-colored water in drained hot tub

[paulitzlee]

I drained my tub the last weekend in September.  I use it in the summer only.

I expect there will always be a little water in the bottom, from rain leakage, condensation, etc...

When I checked the tub this weekend, the water was rust-colored.  I though it strange for water not from the city water supply to be so brown.

My cover MAY be the culprit.  I noticed one of the weep holes has a black plastic washer which came out and was lying in the tub.  I also noticed the stitching came undone on the cover. 
Rust-colored water in drained hot tub


Is it possible for the cover to get dirty inside after a few years, and for the dirt, contaminants, etc... to leak into the hot tub if the weep hole loses its washer?  I think I saw some brown stains around the bottom of the weep hole, but it looks clean now.

I vacuumed the brown water out.  It appears to leave a stain in the tub. Hopefully, the stain won’t affect water quality when I fill the tub in the spring.

For photos, see

https://goo.gl/photos/Sof2pVbL8kE5zAWE7

Please advise.

[av8r]

Rinse the bottom of the cover with fresh water and collect the water.  See what color it is.