Studies on Turbidity, pH and Microbial Presence in Water

Our Objective

Our aim is to study different water bodies for pH, clarity and presence of any living organisms.


Water covers about three-quarters of the earth's surface and it is essential for all known forms of life. Water is a habitat for a variety of plants and animals which have special adaptations to survive in their habitats. Some of the characteristics that control the quality of water are the turbidity of water, pH of water and different types of plants and animals and their density.

Turbidity of Water

Turbidity is the measure of the relative clarity of a liquid. Turbidity of the water body determines the depth to which light can penetrate and thus affects the distribution and photosynthesis of phytoplankton and macrophytes. The more turbid the water body, the less is the thickness of its photic zone (the layer of a body of water that is penetrated by sufficient sunlight for photosynthesis).

Turbidity can be measured using several methods. The easiest and least expensive method is through a Secchi disk. Water turbidity can be measured with a Secchi disk, a circular white or black-and-white disk attached to a tape measure that is lowered through the water to a depth where it disappears from view. In clear lakes, the Secchi depth may be greater than 10 metres, while in eutrophic lakes, with dense growth of algae and other organisms, creating low visibility, the Secchi depth can be less than 1 metre.

pH of Water

The pH is a measure of the relative amount of free hydrogen and hydroxyl ions in an aqueous solution. Solutions with a pH less than 7 are said to be acidic and with a pH greater than 7 are basic. The pH of pure water is 7 at 25°C.

The pH value of a water sample can be determined by indicator dye method and electrometric method using a pH meter. For routine purposes, the indicator dye method, using universal pH indicator solution or paper strips containing the pH indicators, is used.

Living Organisms in Water

The productivity and the trophic state of a water body are determined by quantities of nitrogen, phosphorus, and other biologically useful nutrients. Nitrogen and phosphorus are nutrients that induce plant growth in standing water bodies, so increased concentrations tend to result in increased plant growth.

A productive water body has high nutrient concentrations, and has a very high density of phytoplankton per unit area. These water bodies have high amounts of nutrients and dissolved oxygen and bear large number of organisms at different trophic levels. A water body with a very low density of phytoplankton per unit area is a non-productive water body. The status of health of a water body can be determined by analyzing water samples for the number and type of organisms present in it at a given time.  Such assays also help us to find whether a water body is polluted, as some of the organisms are strong indicators of water pollution. When you look at a water sample with a microscope you will likely see a variety of tiny living things.  Some of them are shown below.

Learning Outcomes

  • Students understand the meaning of turbidity of water, pH of water and about the different living organisms in water bodies.
  • Students understand the term Secchi’s disk.
  • Students do the experiment better in the real lab having gone through the animation and simulation.