Life evolved in the water, then came onto land: probably plants came first, followed by arthropods and amphibians, although this remains open to conjecture.
Water is a polar molecule, a function of its shape with both hydrogen atoms being on one side of the oxygen atom, giving net charges across the molecule.
The average particle in liquid water is more like H8O4 or H6O3 than H2O, as a result of water molecules being linked together by hydrogen bonding.
The key to understanding water and its sometime strange physical properties is the hydrogen bond, which in turn depends on water being a polar molecule.
A porous rock is one with spaces where water can fit, a permeable rock is one where the spaces are linked together, so water can pass through the rock.
Air holds water, and when we measure this atmospheric water, we call it humidity. The whole water cycle relies on variations in the humidity of the atmosphere.
Humidity is measured with a hygrometer and expressed as absolute humidity the amount carried, or as relative humidity, compared with the possible maximum.
Water vapour is a gas, and it is invisible to us. Clouds are masses of condensed water vapour, as is the 'steam' that we see rising from boiling water.
Water droplets form around condensation nuclei: this means that rain water, while it may be fairly pure, necessarily contains a measurable level of impurities.
Water reaches the land in a variety of forms, known collectively as precipitation. Mist and fog are clouds at ground level, and can add to local precipitation.
Precipitation in the fullest sense includes rain, hail, snow, sleet, frost and dew, where 'dew' also includes any condensation from mist and fog.
Precipitation may be measured in either a rain gauge or a precipitation gauge, depending on the climate and precipitation forms at the location of the gauge.
The available water at a particular place depends in part on the rainfall and its regularity, but also on the level of evaporation experienced there.
The water cycle carries salts from the land to the seas, but over time, some ocean salt is lost in subduction zones and some is lost to halite deposits.
Plants need to get water to their highest point, which in some cases, is up to 100 metres above ground, too high for water to get there by simple suction.
Hard water is water with dissolved calcium or magnesium in it: the main effect of hard water may be seen in boiler scale and problems in getting soap to lather.