Vital Zing is a New Zealand born natural flavour enhancer brand that specialises in water drops designed to make hydration more enjoyable, without the downsides of sugar, artificial colours, flavours or preservatives. Their drops use real fruit extracts and natural stevia leaf extract to give flavour and a little touch of sweetness, while keeping carbs, calories, and sugars essentially negligible. Each bottle gives you around 90 serves of flavour, which, in volume, is approx. 18 litres.  They are more cost effective than ready made cordials. Vital Zing also sell soda drops for carbonated water, milk drops and cafe drops for flavoured coffee.