Pick out the filterable impurity in water.

Impurities are any substances that change the natural quality of the water, either positively or negatively. Salt and sugar mixed with water give a taste to water. Chalk powder is an insoluble impurity that settles down as sediment in the bottom of the vessel containing water. It can be filtered out to obtain pure water. Hence, chalk is a filterable impurity, while salt and sugar are soluble impurities.