It is like an Urban Legend that just won't die. My first experience diluting Safeguard in water and it not working was having birds die with high worm loads.
My vet explained to me that since Safeguard was not water soluble that it would not stay suspended and sinks to the bottom of the water where it is unavailable to the birds, it also adheres to the minerals in the water changing the chemical structure and rendering it nearly useless.
Also by not giving a lethal dose and letting some of the worms live is building resistance and eventually the chemical will quit working. Think of it as a doctor telling you to take two aspirin and mix them in a glass of water and take a sip. Two aspirin might work if you took them both but when diluted and not drinking the full glass they are not likely to work.
