Nothing technical....simple run off from shed roof,sheet hard plastic on roof, guttering, down pipes plastic gutter guards
either side of shed, muslin cloth strapped over openings into 4x water butts.In good downpours I have
water as low as 2ppm,very little crap ever gets through, I clean roof and guttering on reg basis.
I have more barrels coming off the house from downpipes front and back, diverters with guttermates
water not as good coming off tiled roof 14ppm onwards..to be honest I don't check guttering out
on reg basis