Water is an inorganic compound with the chemical formula H2O. It is a transparent, tasteless, odourless, and nearly colourless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms. Wikipedia.
All plants and animals need water to survive. There can be no life on earth without water.
And this vintage poster is pushing/promoting the use of tap water in one’s home!! This was not universal in Europe in the 1950s – 60s and still not in many countries in the world today.
