Is your water at home softened, or very soft to begin with?  This indicator
relies on the conductivity of the water, and if you have soft water it won't
conduct well and the indicator will be faint, or won't work at all.  Try
adding a bit of salt to the water and see if it starts working.  I've found
it works great at home, or at campsites with hard water, but I've been to
some that had shallow wells with very soft water and it didn't work at all.