For an explanation, see the main splats page
The principles of water
- 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.
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