This is on a similar theme to "Stertilised water".
A friend has a rain-water butt which got very smelly.
She was told to put Milton in it. I told her I wouldn't use water
containing Milton on my garden!
Is there anything she can use which will remove the smell and not
render the water unusable. Had it been mine the water would not have
stayed there long enough to get smelly!
The butt is fixed on the wall with down pipe connected and not easily
accessible.
TIA

Pam in Bristol