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Water is a transparent and nearly colorless chemical substance that is the main constituent of Earth's streams, lakes, and oceans, and the fluids of most living organisms. Its chemical formula is H2O, meaning that its molecule contains one oxygen and two hydrogen atoms, that are connected by covalent bonds. Water strictly refers to the liquid state of that substance, that prevails at standard ambient temperature and pressure; but it often refers also to its solid state (ice) or its gaseous state (steam or water vapor). It also occurs in nature as snow, glaciers, ice packs and icebergs, clouds, fog, dew, aquifers, and atmospheric humidity.
Water covers 71% of the Earth's surface. It is vital for all known forms of life. On Earth, 96.5% of the planet's crust water is found in seas and oceans, 1.7% in groundwater, 1.7% in glaciers and the ice caps of Antarctica and Greenland, a small fraction in other large water bodies, and 0.001% in the air as vapor, clouds (formed of ice and liquid water suspended in air), and precipitation. Only 2.5% of this water is freshwater, and 98.8% of that water is in ice (excepting ice in clouds) and groundwater. Less than 0.3% of all freshwater is in rivers, lakes, and the atmosphere, and an even smaller amount of the Earth's freshwater (0.003%) is contained within biological bodies and manufactured products. A greater quantity of water is found in the earth's interior.
Water on Earth moves continually through the water cycle of evaporation and transpiration (evapotranspiration), condensation, precipitation, and runoff, usually reaching the sea. Evaporation and transpiration contribute to the precipitation over land. Large amounts of water are also chemically combined or adsorbed in hydrated minerals.
Safe drinking water is essential to humans and other lifeforms even though it provides no calories or organic nutrients. Access to safe drinking water has improved over the last decades in almost every part of the world, but approximately one billion people still lack access to safe water and over 2.5 billion lack access to adequate sanitation. There is a clear correlation between access to safe water and gross domestic product per capita. However, some observers have estimated that by 2025 more than half of the world population will be facing water-based vulnerability. A report, issued in November 2009, suggests that by 2030, in some developing regions of the world, water demand will exceed supply by 50%.
Water plays an important role in the world economy. Approximately 70% of the freshwater used by humans goes to agriculture. Fishing in salt and fresh water bodies is a major source of food for many parts of the world. Much of long-distance trade of commodities (such as oil and natural gas) and manufactured products is transported by boats through seas, rivers, lakes, and canals. Large quantities of water, ice, and steam are used for cooling and heating, in industry and homes. Water is an excellent solvent for a wide variety of chemical substances; as such it is widely used in industrial processes, and in cooking and washing. Water is also central to many sports and other forms of entertainment, such as swimming, pleasure boating, boat racing, surfing, sport fishing, and diving.

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  1. B

    Why Does My Hot Water Circulating Pump Bang When It Starts Up?

    I have recently had a new boiler and circulating pump installed keeping the hot water cylinder. I have the hot water timer set to come on for an hour each morning but when the time is reached, a loud bang comes from the pump which can be heard all over the house. Can anyone please suggest what...
  2. A

    Bath pipe keeps coming away an water comes through kitchen ceiling

    Hello 👋 Just looking for a bit of advice please. Bath waste pipe has a join that over time has come away and when it does water is going straight down the walls dripping form kitchen ceiling below. Got a plumber to look few years back who put the pipe back together an said it shouldn’t happen...
  3. A

    Water hammer despite arrestors being fitted

    Hello I am in a row of 4 houses and we have one stopcock in the street and the pipe divides off to each house and each house has a stopcock under the kitchen floor. The water hammer has been going on for a couple of years and has become gradually worse to a point where I am turning my water...
  4. L

    Help... intermittent hot water issue

    My heating has developed a new and unwelcome quirk just recently, which is that it's sporadically failing to provide hot water. This is something that happened a few weeks back, but it seemed to go back to normal, but in the past couple of days it has happened again each day. We have a...
  5. S

    Vented Hot Water Cylinder Without Vent Pipe!

    After calling a plumber to look at our leaking power shower he discovered that there is no vent pipe coming off the hot water cylinder . The cylinder is an old indirect vented cylinder heated from the central heating boiler and has a secondary electric immersion heater that is disconnected...
  6. T

    Worcester Greenstar 30CDi info please

    Hi Is the Eco button for the heating of the radiators, or the domestic Hot water? The reason i ask is there is also an E setting on the Hot water control Knob. When i had a Baxi(old house), the domestic hot water always had priority. which seems logical. How does a worcester bosch handle it...
  7. M

    Hot radiators remain when heating goes off - maybe from hot water storage cylinder ?

    Hot water coming out of the hot water storage cylinder into upstairs radiators after heating/HW turns off and running out of hot water in the mornings. I have a Glow Worm 24HX Condensing boiler on the ground floor with a pump in the same cupboard, a hot water storage cylinder in the airing...
  8. Andrew Stride

    URGENT An old mains stopcock on an 30mm pipe needs replacing, please help.

    I need to replace the stopcock on an old mains water pipe. The house is about 60 years old, the pipes OD is 30mm, my local plum centre said they had no parts available to do this. The old stopcock is leaking and seized solid. Any advice about where I can get the parts to fix the problem would...
  9. L

    Question on upgrading hot water cylinder

    Hello, I am looking into upgrading various parts of my residential block's heating and hot water system, which serves 12 flats that resulted from the conversion of two adjacent terraced houses. Our current hot water cylinder has 1000 lts capacity, is vented, is heated indirectly through a gas...
  10. elvis80

    PEX-AL-PEX for hot water return (manifold system)

    (Bear with me this is my first post on here...) We're putting in a manifold system for the H+C in the bathrooms of our new house (self-build). What are everyone's opinions on using PEX-AL-PEX pipe for our hot water return system, please? Good or bad idea? The pipe says: Tmax 95 degrees C / 10...
  11. S

    Valliant ecotec 637 no water sign on display and radiator flashing

    Hi. i have new installed valliant ecotec 637. The tap button is not showing on the display and the radiator is flashing on the screen. I can press the right button and change all the radiator settings but I am unable to access any of the tap settings as there is nothing on display. Please help!
  12. D

    Steam box in shower gushing water

    We have a monstrosity of a shower which has all these unnecessary features, like jets and steam. The steamer hasn't worked in years, but recently the little steam box at the bottom of the shower has started gushing water when the power is turned on. I don't need the steam to work, but I would...
  13. S

    Black Specks in Water (only on 2nd floor)

    I'm getting black specks in my water when running hot water, but it is only on my second floor. We have well water with a salt water softener. The specks are more oil-like and smear if I press my finger on them. The specks come out when I run the hot water (hotter the water = more specks). It...
  14. S

    Getting a Remote Control RFWRT thermostat talking to a Worcester Boiler 28i

    Getting a Remote Control RFWRT thermostat talking to a Worcester Boiler 28i, changed the batteries, no heating, hot water working ?
  15. M

    Thermal store combi boiler, hot water flow rate.

    Can anyone tell me the hot water flow rate on a thermal store combi boiler? As opposed. To a 40kw combi that will deliver nearly 16litres per minute. And any recommendations for a good thermal store boiler thanks.
  16. P

    Cold water feed tanks - bowing wood supports - advice on options

    Hi all, We had an old gravity fed system and the loft has two huge cold feed tanks that are joined at the base, we have moved the cold water supply to mains so the tanks now only feed the hot water cylinder. The problem is the two tanks are big and the wood frame underneath is bowing badly...
  17. R

    URGENT Zero water pressure on boiler gauge

    Gas boiler shows No Water Pressure. The water feed to feed the system doesn't move gauge. Water dumps overboard. A banging noise starts when the valve to top up the system is opened.
  18. C

    Heating / hot water glitch ?

    Good day . The heating and hot water on my vaillant boiler work fine independently . If my heating is on and a hot water tap is opened or shower used - the heating [ if on ] refuses to come back on and if left will stay off . If I hit the reset button the boiler will fire and the heating comes...
  19. C

    Heating won't come back on after using hot water tap / shower

    Good evening . I have a Vaillant boiler that although the heating and hot water work perfectly independently the heating if in use will not come back on after using a hot tap or shower . If I press the reset button the heating will come back on but will not do so on it's own accord . Any advice...
  20. Bbarclays

    No hot water open vent glowworm fuelsaverMKII R40

    Hi there Today friend was changing radiator valves, so he drained system, put radiator valves, new radiator. I notice TRV valve was on cold end- return or out line from radiator. I asked my friend to relocate TRV valve on inlet side. (when heating started, hot water was coming from white plastic...