Er, water? Wherever it comes from there will be supposedly some sort of risk whether it be from a natural underground spring (what nasties has it picked up along the way?), treated water (no guarantees there), bottled water (does it react in some way with plastic?), rainwater (acid pollution?), distilled, de-ionised and boiled water (probably no fluorides left so tooth decay will be more prevalent) so we're left with so answers on a dew-drop please!