Water Quality Analysis Lab

 Comparison Between a Rock Creek Sample with Other DC Site


Water Quality Lab Report (75 points)

Each of the bold parts below are used as section headings in your lab report. Your report should be in a 12-point font, double-spaced and no longer than five pages (including the tables). Consult the lab report rubric in addition to the details below.

Title (make it specific to the topic and your water sample)

Introduction: In one paragraph include the following:

  • Provide at least three pieces of background information on the importance of clean water and how the quality of water is tested. Cite your sources!
  • State the hypothesis and prediction about your particular water sample. Make sure your hypothesis has an explicit justification and is not just a guess or your opinion. Use sources to convince your reader!
  • One or two sentences to connect your background information with the importance of your hypothesis and your prediction for the experiment.

Materials and Methods

State which assays you performed and the positive and negative controls for each. Make sure you use past tense and do not include a materials list or any reference to containers!


Include a description of the water sample and the source of the water. Summarize the results of your water sample at every station, citing your data tables (1-3). Include the following data tables in your results section.

Table 1: Water Sample Results

Testing Form




Sample  1


Sample 2 


Sample 3


Sample 4


Sample 5


Sample 6




Nitrites (ppm)
Nitrates (ppm)


Table 2: Presence of Bacteria

Sample: _______ # colonies/ plate
E. coli (dark blue/ purple colonies)
# Other colifoms (pink/ red colonies)
# of other bacteria (green colonies)


Table 3: Dissolved Oxygen Calculations

Sample: _______ # aliquots (total volume)
Number of 1mL Thiosulfate aliquots
Number of 100 uL Thiosulfate aliquots
Total volume (in mL) Thiosulfate added
Calculate dissolved oxygen in sample using the following conversion rate –
1 mL Thiosulfate added = 6 mg of oxygen/L (liter)


  • Summarize ways in which the water can be affected by the environment. How did this influence your hypothesis and prediction?
  • Describe how your results supported or refuted your hypothesis and your prediction. You may also need to explain why results were inconclusive. Make sure to include the outcome of positive and negative controls if results are inconclusive.
  • Describe any problems or issues with observing and quantifying the assays, oxygen titration, and coliform bacteria colony growth.
  • If water is clear and smells fresh, can you consider it safe to drink? Give two reasons why or why not.
  • Look up the Clean Water Act that congress established in 1972. Is it still important to current day?
  • In a couple of sentences, write a conclusion about the importance of safe drinking water in terms of globalization and the biological significance to growing human populations.

References: You should use at least 3 outside references (in addition to your lab manual). Cite these in the text as you reference them. Want to cite this manual?




Water is vital for life. Not only do we need water to drink, to grow foods and to wash, but it is also important for many of the pleasant recreational aspects of life. Each different use has its own requirements over the composition and purity of the water and each body of water to be used will need to be analyzed on a regular basis to confirm its suitability. Nowhere in the environment can you consider water to be chemically pure. There are several chemical species dissolved in water, including gasses. (Reeve, 2002) In the following report, we are going to summarize seven chemical parameters (iron, chlorine, ammonia, dissolved oxygen, calcium and magnesium, pH and nitrate) and three biological parameters (bacteria count as E. Coli, coliforms and other bacteria). Oxygen is vital in supporting aquatic life. A fast-flowing turbulent river will usually be saturated in atmospheric gases. Oxygen levels in water are depleted by slow oxidation of organic and some inorganic material. The presence of large quantities of oxidable organic materials (e.g. from sewage effluents) is often the most serious form of pollution in watercourses. The pH is related to the number of hydrogen ions in solution. At the low concentrations of hydrogen ions and low ionic strengths, which are typical of unpolluted environmental samples, the hydrogen ion activity is approximately equivalent to the hydrogen ion concentration. The magnesium and calcium ions are representative for water hardness, this effect is produced from the weathering of minerals and are often based on carbonates. (Reeve, 2002) Chlorine is produced in large amounts and widely used both industrially and domestically as an important disinfectant and bleach. It is widely used in the disinfection of swimming pools and is the most commonly used disinfectant and oxidant in drinking-water treatment.  (WHO, 2004) Nitrogen (present in water system, in the form of ions like ammonium and nitrate) plays a highly significant role within the earth system. Regardless of the specific ecosystem, fertilization of the soil with nitrogen has an enormous impact on the growth yield of plant life; therefore, the animals and other species that depends from plants. Nitrogen is by far the most commonly applied nutrient in an agricultural setting. (Schlager & Knight, 2002) Since December 2006, the U.S. Geological Service, in cooperation with Montgomery County Department of Environmental Protection and National Parks Service, began with the project of the water-quality monitoring in Rock Creek Park, Washington, DC. They analyze over fifteen parameters monthly, (nutrients, particulate carbon, dissolved chlorine, E. Coli, total suspended solids and suspended sediments) and five real-time parameters (water temperature, pH, specific conductance, dissolved oxygen and turbidity). (“USGS Projects – Water-Quality Monitoring in Rock Creek Park, Washington, D.C.”, 2017) Due the nature of the water sample, from a protected natural area that has been monitoring for several years, we can predict that the parameters related to nutrients, bacteria and chlorine will be low, (we can suppose that there isn’t any significant contamination source around this water body) and a high dissolved oxygen concentration (due his tropic state, that presumably will be oligotrophic).


Materials and Methods:

We tested seven chemical parameters in five sample sites and three biological parameters in the site of our focus. The chemical parameters and the assay used were the following: 1. Iron. Five drops of sulfuric acid and a small scoop of ammonium thiocyanate were added to each sample. This is a qualitative test and the positive result is the change of coloration to a deep red color, indicating the formation of the complex of iron (III) and thiocyanate. We made a positive control with ferric chlorine and a negative test with deionized water. 2. Chlorine. Three drops of o-tolidine were added to each sample. This is a qualitative test and the positive result is the change of coloration to a yellow color, in small concentrations of chlorine, to a reddish-brown color, for high concentrations. We made a positive control with chlorine bleach and a negative test with deionized water. 3. Ammonia.  Two drops of ammonia test solution #1 and two drops of solution #2 were added to every water sample. The color developed was compared in a color chart to determine the concentration of ammonia present. We made a positive control with ammonium chloride and a negative test with deionized water. 4. Calcium and Magnesium (Water hardness) Five drops of ammonium hydroxide, two drops of indicator solution and five drops of EDTA (in this sequential order) were added to every water sample. A positive result is the change of coloration from blue to pink, indicating the formation of complex between the indicator and the alkaline earth metals. We made a positive control with a mixture of magnesium and calcium chloride and a negative test with deionized water. 5. Dissolved Oxygen. We performed to every sample the Winkler method, a titration of 50mL pretreated sample with a sodium thiosulfate solution, with a stoichiometric relationship of 1mL of thiosulfate solution equals to six milligrams of dissolved oxygen per liter. 6. PH. We added two drops of universal indicator to every sample. The color developed were compared to a color chart to determine the pH of the solution. 7. Nitrate. Two drops of nitrate test solution #1 and two drops of solution #2 were added to every water sample. The color developed was compared to a color chart to determine the pH of the solution. The biological parameters determined in this study were the following: Determination of presence of bacteria (E. coli, coliforms and other bacteria) by growth development in a petri dish with agar-supported medium that was mixed with specific reagents for the identification of E. coli and coliforms. The samples were incubated at 35°C for 24 hours. After incubation, the formation colony units (fcu) were counted.




Table 1: Water Sample Results

Chemical Positive






1 2 3 4 5
Anacostia River Rock Creek Aquarium Koi Pond DC Tap
Iron Ferric Chloride: Positive Deionized Water: Negative Negative Negative Negative Negative Negative
Chlorine Chlorine Bleach: Negative Deionized Water: Negative Negative Negative Negative Negative Negative
Ammonia Ammonium Chloride: Positive Deionized Water: Negative, 0 1.5 4 0.25 0.25 0.25



Calcium and Magnesium Chloride: Positive Deionized Water: Negative Negative Positive Positive Positive Positive
pH 7 7 7.5 7 7
Nitrates (ppm) 5 0 0.25 0 5
ppm O2 21 20.4 25.4 24 35.4


Table 2: Presence of Bacteria

Sample: Rock Creek # colonies/ plate
# E. coli (dark blue/ purple colonies) 1
# Other coliforms (pink/ red colonies) 15
# of other bacteria (green colonies) 0


Table 3: Dissolved Oxygen Data for Calculations

Sample: Rock Creek Total Number Total Volume (in mL)
# of 1 mL aliquots of Na Thiosulfate added 3 3.0mL
# of 100μL aliquots of Na Thiosulfate added 4 0.4mL
Total volume of Na Thiosulfate in mL N/A 3.4mL



The high discrepancy between the results and the highest reported value for dissolved oxygen, Theoretically, a saturated water at 25°C and 1atm pressure contains 8.54mgL-1 oxygen (Reeve, 2002), could be result of bad sampling (to let air bubbles inside the bottle), addition to air bubbles between the addition of reagents, presence of oxidizing ions that could serve as interference to the method or an incorrect stoichiometry relationship of the sodium thiosulphate solution and the dissolved oxygen (It could be necessary to standardize again the solution). Data from USGS web site shows that in the period from October 2015 to September 2016, the maximum average value registered was 12.9mgL-1 reported on December 2015. (“USGS Water-Year Summary for Site 01648010”, 2017). The fact that the positive control for the chlorine analysis resulted negative, impacts the credibility of the results obtained. It is only possible to determine that the levels of chlorine in the samples are lower to the concentration of chlorine in the solution of water bleach. The high presence of ammonia ions and the absence of nitrate ions could indicate a contamination from agricultural practices. The presence of magnesium and calcium ions, indicate an environment influence by the surrounding minerals and the presence of carbonates, that shifts the pH from 5.6 (the theoretical pH of water in equilibrium with the atmosphere) to 7.0, classifying it in soft water. Our prediction failed in the concentration of nutrients that could lead to a contamination source. It was not possible to find the data reported from USGS in order to support our results. Therefore, it is important to continue the monitoring of this variable to look for trends and confirmation of the data reported.


The Clean Water Act (CWA) establishes the basic structure for regulating discharges of pollutants into the waters of the United States and regulating quality standards for surface waters. (“Summary of the Clean Water Act | US EPA”, 2017).  Since 1972, the act had several amends with the purpose of giving resources to the United States Environmental Protection Agency (EPA) in the fulfillment of the objectives of this act. It is important that federal agencies like EPA should continue with this labor to ensure the quality standards that can ensure the protection and sustainability of the environment, and clean water to the American citizens. It is important to notice that not all the parameters involved in the water quality analysis are volatile or colored, meaning that the visual and odor inspection is not enough to declare that a sample is safe to drink.


As a conclusion, the growing of human population depends of the quality of their resources and the water quality is vital for human development. Safe drinking water can be assured by several chemical, biological and physical that needs to be monitoring frequently, due the constant change in composition of this resource. Giving the tools and adequate financing to governmental agencies to monitoring these parameters, guarantee our health and sustainability to the future as a society and civilization.



  • Reeve, R. (2002). Introduction to environmental analysis (pp. 35-37, 55-57). New York: Wiley.
  • Schlager, N., & Knight, J. (2002). Science of everyday things, Vol. 4 (pp. 334-335). Detroit: Thompson Gale Group.
  • Summary of the Clean Water Act | US EPA. (2017). US EPA. Retrieved 27 September 2017, from https://www.epa.gov/laws-regulations/summary-clean-water-act
  • USGS Projects – Water-Quality Monitoring in Rock Creek Park, Washington, D.C. (2017). Md.water.usgs.gov. Retrieved 27 September 2017, from https://md.water.usgs.gov/projects/qw/rock_creek/index.html
  • USGS Water-Year Summary for Site 01648010. (2017). Waterdata.usgs.gov. Retrieved 27 September 2017, from https://waterdata.usgs.gov/nwis/wys_rpt/?site_no=01648010
  • (2004). Guidelines for drinking-water quality, Vol1. (3rd ed.). Geneva: World Health Organization.