Re: Water Fast And Physical Work, Please Help!
As long as you don't ingest anything except water, and break the fast safely, you don't do any harm to your body. If you were being sick and had diarroah for more than a short while, and were unable to keep water down, that would be a reason to break the fast. The body keeps everything in balance during a fast, but if that happened you could lose valuable mineral salts ie electrolytes.
Sudden weakness may indicate this as well, with the emphasis on sudden, as general weakness is to be expected at times during the fast.
As for toothpaste, i don't think you have ruined your fast, use bicarb from now on, and use a less harsh shampoo. I suppose because of the manual work you do, you have to shower and wash hair. I know some people just use water, but i would feel dirty, and i could not go without showering. Try to wash hair less frequently though. Others may disagree.