question: Why does tap water taste different, stale, if it sits out for a while?
comment: There are a few reasons it might taste different. First is temperature. Water coming out of the tap will usually be a little cool. And cold can help mask the metallic flavor of the minerals in your tap water. Leaving a glass of water out lets the water warm up and changes its flavor. Next is aeration. Water coming out of your tap can have a lot of air dissolved in it from being under pressure. This is why there are some bubbles in your water. Those gases can have an effect on the taste. Letting the glass sit for a while gives the gases a chance to escape and changes the flavor. Finally, if 'for a while' means a day, the taste change is probably due to microorganisms that are starting to grow in the water.
passages: Specific chemical compounds are often taken out of tap water during the treatment process to adjust the pH or remove contaminants, and chlorine may be added to kill biological toxins. Local geological conditions affecting groundwater are determining factors for the presence of various metal ions, often rendering the water "soft" or "hard".
   Section::::Common drinking water contaminants.
   BULLET::::- Maximum Nitrogen Concentration (NH4-N [micro l-1] of 13 on the surface and 120 at the bottom of the lake have been reported.
  
  BULLET::::- The lake water temperature varied from a minimum of in January to in June/July at the surface and correspondingly and , at the bottom of the lake.
  
  Section::::Water quality issues.:Flora.
  
  Within the lake water, the flora recorded comprise the following.
   Tap water can sometimes appear cloudy, often mistaken for mineral impurities in the water. It is usually caused by air bubbles coming out of solution due to change in temperature or pressure. Because cold water holds more air than warm water, small bubbles will appear in water. It has a high dissolved gas content that is heated or depressurized, which reduces how much dissolved gas the water can hold. The harmless cloudiness of the water disappears quickly as the gas is released from the water.
  
  Section::::Hot water supply.
   Water. It's necessary to sustain life, but to many Casual Dining restaurant chains it contributes to a dull dining experience for the customer. Many customers choose tap water not because they enjoy it, but because it is what they always have drunk in the past. In response, some restaurant chains are implementing programs to help train crews to sell alternative choices to tap water, like soft drinks and non-carbonated beverages, with the goal of increasing overall guest satisfaction. 
   Tap water remains susceptible to biological or chemical contamination. In the event of contamination deemed dangerous to public health, government officials typically issue an advisory regarding water consumption. In the case of biological contamination, residents are usually advised to boil their water before consumption or to use bottled water as an alternative. In the case of chemical contamination, residents may be advised to refrain from consuming tap water entirely until the matter is resolved.
   Purified water is also used in the commercial beverage industry as the primary ingredient of any given trademarked bottling formula, in order to maintain critical consistency of taste, clarity, and color. This guarantees the consumer complete reliability of safety and drinking-satisfaction of their favorite refreshment, no matter where in the world it has been bottled. In the process prior to filling and sealing, individual bottles are always rinsed with deionised water to remove any particles that could cause a change in taste.
   BULLET::::- fossil water – groundwater that has remained in an aquifer for thousands or millions of years; when geologic changes seal the aquifer preventing further replenishment, the water becomes trapped inside and is then referred to as fossil water. Fossil water is a limited resource and can only be used once.
   Section::::Hard Water becomes Soft Water.
   The water renews every 2 days. The average pH is 7.5 and the salt content is 2.5%. Very few organisms live in the water apart from some blue-green algae, despite the water not being artifically disinfected it contains no fecal bacteria, environmental bacteria, fungi, or plants.
  
  Section::::History.:Baths.
   Some plants prefer flowing water, while others, such as lotuses, prefer stagnant water.
  
  Various anaerobic bacteria are commonly found in stagnant water . For this reason, pools of stagnant water have historically been used in processing hemp and some other fiber crops, as well as linden bark used for making bast shoes. Several weeks of soaking makes bast fibers easily separable due to bacterial and fermentative processes known as retting.
  
  BULLET::::- Denitrifying bacteria
  
  BULLET::::- Leptospira
  
  BULLET::::- Purple bacteria (both sulfur and non-sulfur)
  
  Section::::Life that may thrive in stagnant water.:Fish.
  
  BULLET::::- Lepisosteidae (gar)
  
  BULLET::::- Northern snakehead fish
  
  BULLET::::- Pygmy gourami
   BULLET::::5. Filtration: Settled water from the sedimentation basins is treated with a filter aid polymer and enters the filters, which consist of layers of anthracite coal, sand, and gravel filter media. The filters remove smaller particles from the water as well as larger particles that did not settle during the sedimentation process.
   The water table at Chernobyl Nuclear Power Plant fluctuates from on average in December to on average in May.
   During high turbidity peaks, pathogens are more commonly found in raw water. This can contribute to the spread of illnesses. When turbidity increases, reported hospital visits for the elderly (65+) with gastrointestinal illnesses also increase. Even places with water filtration systems that meet standards can have an endemic of gastrointestinal illness, or waterborne infectious diseases. Those hospitalized represent a small percentage of total morbidity caused by these illnesses.
  
  Section::::Turbidity.:Controlling turbidity.
   Drinking water quality has a micro-biological and a physico-chemical dimension. There are thousands of parameters of water quality. In public water supply systems water should, at a minimum, be disinfected—most commonly through the use of chlorination or the use of ultra violet light—or it may need to undergo treatment, especially in the case of surface water. For more details, please see the separate entries on water quality, water treatment and drinking water.
  
  Section::::Service quality.:Water pressure.
   In the developed world, levels of contaminants found in tap water vary for every household and plumbing system but tend to be low. Two general conceptions with popular appeal are:
  
  BULLET::::1. That tap water is widely contaminated
  
  BULLET::::2. That bottled water is assuredly pure
   Over time, calcium from municipal water tends to accumulate, developing salt deposits in the swimming pool walls and equipment (filters, pumps), reducing their effectiveness. Therefore, it is advised to either completely drain the pool, and refill it with fresh water, or recycle the existing pool water, using reverse osmosis. The advantage of the latter method is that 90% of the water can be reused.
  
  Pool operators must also store and handle cleaning and sanitation chemicals safely.
  
  Section::::Prevention of diseases in swimming pools and spas.
   Contaminants that may be in untreated water include microorganisms such as viruses, protozoa and bacteria; inorganic contaminants such as salts and metals; organic chemical contaminants from industrial processes and petroleum use; pesticides and herbicides; and radioactive contaminants. Water quality depends on the local geology and ecosystem, as well as human uses such as sewage dispersion, industrial pollution, use of water bodies as a heat sink, and overuse (which may lower the level of the water).
   Section::::Water stress.:Changes in climate.
   The electricity also fluctuates multiple times. The tap water overflows and comes out of the main door. Neighbors see the water, but they think the owners are on holiday.
   Food designers use water activity to formulate shelf-stable food. If a product is kept below a certain water activity, then mold growth is inhibited. This results in a longer shelf life.
  
  Water activity values can also help limit moisture migration within a food product made with different ingredients. If raisins of a higher water activity are packaged with bran flakes of a lower water activity, the water from the raisins migrates to the bran flakes over time, making the raisins hard and the bran flakes soggy. Food formulators use water activity to predict how much moisture migration affects their product.
   As water passes through the distribution system, the water quality can degrade by chemical reactions and biological processes. Corrosion of metal pipe materials in the distribution system can cause the release of metals into the water with undesirable aesthetic and health effects. Release of iron from unlined iron pipes can result in customer reports of "red water" at the tap. Release of copper from copper pipes can result in customer reports of "blue water" and/or a metallic taste. Release of lead can occur from the solder used to join copper pipe together or from brass fixtures. Copper and lead levels at the consumer's tap are regulated to protect consumer health.
   A variety of nutrient cycles is important in the aquarium. Dissolved oxygen enters at the surface water-air interface through agitation or what would be observed as waves in a natural environment, and Carbon dioxide escapes into the air. The phosphate cycle is an important, although often overlooked, nutrient cycle. Sulfur, iron, and micronutrients enter the system as food and exit as waste. Appropriate handling of the nitrogen cycle, along with a balanced food supply and consideration of biological loading, is usually enough to keep these nutrient cycles in adequate equilibrium.
  
  Section::::Aquarium maintenance.:Water conditions.
   Groundwater can be a long-term 'reservoir' of the natural water cycle (with residence times from days to millennia), as opposed to short-term water reservoirs like the atmosphere and fresh surface water (which have residence times from minutes to years). The figure shows how deep groundwater (which is quite distant from the surface recharge) can take a very long time to complete its natural cycle.
   In some regions, for example, Great Britain or California, winter precipitation is often higher than summer precipitation and so the groundwater storage is not fully recharged in summer. Consequently, the water table is lower during the summer. This disparity between the level of the winter and summer water table is known as the "zone of intermittent saturation", wherein the water table will fluctuate in response to climatic conditions.
  
  Section::::Fluctuations.:Long-term fluctuations.
  