What is in Tap Water?

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Author: Michael Calhoun

Grade Level: 2nd - 4th; Type: Physical Science


What is the project about?

Tap water usually contains dissolved gases notably air which is composed mainly of nitrogen and oxygen, along with some carbon dioxide, so when the tap water is allowed to stand some of the dissolved air comes out of the water because liquids in general release dissolved gas as they warm up. This science fair project will illustrate that gases are dissolved in most natural and municipal water.

What are the goals?

Water samples as diverse as tap water to rainwater will be placed in drinking glasses and allowed to sit in a warm place, after a time, bubbles will be seen collecting on the sides of the glass indicating the release of dissolved gases. Based on the results of this investigation a data table will be prepared and the results potted on a graph. A practical benefit gained from conducting this investigation is that the young investigator will be to answer the question "why is the water from the tap bubbly."

Research Questions:

  • Which water sample produced the most bubbles?
  • Which water sample did not produce bubbles?
  • Which water sample produced bubbles the longest and what does this mean?
  • Why is the water from the tap bubbly?
  • Which water sample is the control for this science fair investigation?

Cloudy water from the tap, also known as "white water" as seen in the photograph below, is caused by air bubbles in the water. As the water cools the dissolved air is released to the atmosphere and the bubbling eventually stops. Cold or cool water holds more air than warm water.

In the case of tap water it usually travels from an underground aquifer or reservoir which is cooler than its surroundings for the most part and warms up during its travel to the tap. The air that is present is no longer soluble, and comes out of solution. In addition, once water from a reservoir enters the transmission and distribution pipes, the water is pressurized. Water under pressure holds more air than water that is not pressurized. Once the water comes out of the tap it is no longer under pressure and the air comes out of solution as bubbles (similar to a carbonated soft drink).

Water from almost any source (streams, ponds, lakes, rivers, etc) that is exposed to atmospheric gases (air, carbon dioxide, etc) will act as a solvent and dissolve these gases. The lower the temperature to more gas it can absorb. As the temperature of the water increases, it cannot hold so much gas in solution and some of it separates.

Distilled water if kept in a container free from contact with air after it is goes through the distillation process, is pure water and will not produce bubbles as it cools, distilled water has a flat taste, because air and other dissolved substances which give water its taste have been removed.

Rain is water which has been evaporated from the surfaces of natural bodies of water, oceans, lakes, and from the land, is practically free from particulate material, but contains dissolved gases. The first fall of any shower is mixed with impurities which have been washed from the air. Among these may be carbon dioxide, ammonia, and carbon in the form of soot and creosote.

Most commercial bottled water comes from the same sources as tap water, and like tap water will contain dissolved gasses which will be released upon standing in a warm area. Whether the water is coming out of the tap or from the bottle the amount of dissolved gas depends largely on geographical location and the municipal treatment facility.

Any required diagrams/pictures (Pictures speak a thousand words!)

Digital photos can be taken during the investigating process also the following sites offer down loadable images that can be used on the display board:

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