Hi Dave,
That rain water will be fine. Raindrops form around particles in the air before they drop to the ground. Thats why sometimes you see on cars fine dust deposits where the raindrops have dried off.
If you plan to use the water from this butt, they forecast rain for the whole Uk (about time too!) so it maybe an idea to clean out any unwanted debris/dirt from there and start fresh
That rain water will be fine. Raindrops form around particles in the air before they drop to the ground. Thats why sometimes you see on cars fine dust deposits where the raindrops have dried off.
If you plan to use the water from this butt, they forecast rain for the whole Uk (about time too!) so it maybe an idea to clean out any unwanted debris/dirt from there and start fresh