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it's the only substance on Earth that commonly exists in large amounts in all 3 physical states
many substances are easily dispersed throughout the environment because they are soluble in water - once dissolved, it is not easy to remove substances from water
it is the only common liquid on the surface of our planet
the solid form of water (ice) is less dense than the liquid - meaning it expands as it freezes
ice forms on the surfaces of lakes and insulates the lower layers of water which enables fish and other aquatic organisms to survive winter in the temperate zones
when living tissues freeze, ice crystals are formed and the expansion ruptures and kills cells - the slower the cooling, the larger the crystals, and the more dangerous ice is to cells
water is also more dense than most other familiar liquids - most other things float on the surface
it has a high specific heat and large capacity to store energy absorbed as heat
the vast amounts of water on the surface of Earth act as giant heat reservoirs to moderate daily temperature variations
the structure is unique and it is a highly polar molecule and able to dissolve many things |
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| the quantity of heat energy required to change the temperature of 1 g of a substance 1 degree celsuis |
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water has a high one - the heat required for a liquid to transform into a gas
a large amount of heat is required to evaporate a small amount of water - this is enormously important as large amounts of body heat can be dissipated by the evaporation of small amounts of water (SWEATING) from skin to maintain our internal temperatures |
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98% of water in nature is salty seawater - due to water's polar nature and its ability to dissolve most ionic substances
rainwater dissolves minerals that are carried by streams and rivers to the sea, where the sun's heat evaporates some water and leaves the salty concentration higher
2% of earth's water is frozen in polar ice caps
1% of earth's water is fresh - mostly underground
.01% of earth's FRESH water is in lakes and streams |
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| water is dynamically cycled among various repositories, constantly evaporating from both water and land surfaces, water vapor condenses into clouds and returns to earth as rain, sleet and snow |
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rainwater is not pure H2O - it carries down dust particles, dissolved oxygen, nitrogen, and CO2 as it falls through the atmosphere, making it slightly acidic as it forms carbonic acid by reacting CO2 and water (H2CO3)
lightning causes nitrogen, oxygen, and water vapor to combine to form nitric acid, which dissolves in rainwater as well |
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| dissolved minerals in water |
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as water moves along or beneath the surface of Earth, it dissolves minerals from rocks & soil
rainwater dissolves matter from decaying plants and animals - in small quantities it is part of the natural cycle in a forest and entiches the soil, but in large quantities it contaminates soil and water |
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water containing calcium, magnesium, or iron salts
the positive ions react with negative ions in soap to form a scum that clings to clothes and bathroom fixtures |
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| water that may contain ions (Na+, K+) but that do not form scum |
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| an estimated 80% of all the world's sickness is caused by contaminated water |
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acids formed from sulfur oxides and nitrogen oxides come down from the sky as acid rain, fog, snow, etc.
they corrode metals, dissolve limestone and marble, and ruin the finishes on many things
they also flow into streams from abandoned mines - and coal fired power plants
acids are no threat to lakes and streams where limestone (calcium carbonate) is plentiful - limestone neutralizes excess acid |
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exists in water, gets depleted when bacteria breakdown organic matter in the water
biodegradation can either be aerobic or anaerobic |
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| occurs in the presence of dissolved oxygen |
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| Biochemical oxygen demand |
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BOD - a measure of the amount of oxygen needed for biodegradation in any one place
the greater the amount of degradable organic wastes, the higher the BOD
if the BOD is high enough, dissolved oxygen gets depleted and no life (other than anaerobic bacteria) can survive |
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| when algae die and become organic waste and increase BOD - leaving an excess of organic matter and a depletion of dissolved oxygen, leading to suffocation of everything living in the lake/stream |
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| when no dissolved oxygen is available, anaerobic bacteria reduce organic matter and form methane CH4, and convert sulfur to hydrogen sulfide H2S rather than oxidizing it - only anaerobic microorganisms can survive in this state |
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| to make 1 metric ton of steel |
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| about 100 tons of water is required - wasting water excessively in all kinds of manufacturing |
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certified to have been produced without synthetic pesticides or fertilizers
some types use what is otherwise waste from agricultural production (soy fiber) |
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| groundwater contamination |
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it is particularly alarming because once contaminated an underground aquifer may remain unusable for decades or longer - there is no easy way to remove contaminants
nitrates in groundwater come from fertilizers used on farms and lawns, from decomposition of organic wastes in sewage treatment, and runoff from animal feed lots - they are highly soluble and difficult to remove from water, requiring excessive treatment, and are especially dangerous to infants
volatile organic compounds (VOCs) can also be water pollutants and are suspected carcinogens
underground storage tanks (USTs) have an average life span of 15 years before they rust through and begin to leak |
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passed in 1974 and amended in 1986 and 1996 - gives EPA power to set, monitor, enforce national health-based standards for a variety of contaminants in municipal water supplies
regulated substances with maximum contaminant levels (MCLs) increased from 22 to 90 in 2004 |
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| parts per million / parts per billion |
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for aqueous solutions, ppm, ppb, and ppt are generally based on mass
1 ppm of solute in a solution is the same as 1 g solute per 1 million grams solution, and 1 ppb is 1 gram solute per 1 billion grams solution |
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| most cities in developed nations treat their water supply before it flows into homes - usually bu aeration (spraying it into the air to remove odors and improve taste with dissolved gases from air) |
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chlorine is added to kill any remaining bacteria post aeration
some people question the use of chlorine because it converts dissolved organic compounds into chlorinated hydrocarbons
chlorination is not the only way to disinfect drinking water - OZONE is used widely in Europe - it is more expensive but less is needed, and it kills viruses on which chlorine has no effect
Ozone works by transferring its 3rd oxygen atom to the contaminant - oxidized contaminants are generally less toxic than chlorinated ones - and ozone imparts no chemical taste, but it does not provide residual protection against microorganisms
also water can be purified of a variety of microorganisms by irradiation with UV light - no chemical generation, storage, or handling is required - but has no residual protection for drinking water and no taste or odor control |
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added to water to help increase hardness of tooth enamel and prevent decay
fluoride ions replace some of the hydroxide ions in tooth enamel, forming a harder mineral called fluorapaptite
but fluoride salts (NaF) are acute poisons in moderate to high concentrations |
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| wastewater treatment plants |
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PRIMARY SEWAGE TREATMENT - holding sewage in settling ponds for a while before discharging it into another body of water, removes 40% to 60% suspended solids as sludge and 30% of organic matter - with this step, all the dissolved oxygen in the pond may be used up, and anaerobic decomposition (with its odors) takes over
SECONDARY SEWAGE TREATMENT - passes effluent from the primary treatment facility through sand and gravel filters - with some aeration
ACTIVATED SLUDGE METHOD - a combination of primary and secondary treatment methods, sewage in tanks is treated by large aerator blowers, forming clumps that get filtered out - sludge must be removed for disposal
ADVANCED TREATMENT - continued treatment after secondary - charcoal filtration (charcoal absorbs organic molecules), reverse osmosis (pressure forces water through semipermeable membrane), phytoremediation (in lagoons for storage, allowing for plants to remove contaminants) |
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costs 240 to 10,000 x as much as tap water per liter
but more than 1/2 all Americans drink it
misconception that is healthier or safer - the testing of bottled water is typically less rigorous as it is a product
25% of bottled water sold in US is from the tap
mineral water has more dissolved ions than tap water |
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