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Water Sampling Techniques From a Lake for Microbiological Analysis

Lake water may be sampled for microbiological analysis for many reasons. You can determine the health of the lake ecosystem by measuring the amount of phytoplankton present. These are microscopic photosynthetic organisms that are the primary producers in most aquatic ecosystems. You may also be interested in testing for contamination from industrial waste or for the presence of algal blooms.

Build a Sampler
- To make a simple water sampler, attach a plastic cup to the end of a PVC tube. Drill two holes at the end of the tube and two matching holes in the cup. Attach the cup with bolts and nuts through the holes in the PVC. Mark the PVC so that you can determine the depth of the water the sample is drawn from. This apparatus is also handy for reaching the water without having to get too close to the edge, thus reducing the possibility for accidents.
Obtaining the Sample
- Rinse your sampler with distilled water three times before taking your sample. Lower your sampler into the lake and obtain your sample. Transfer the sample to a sterile test tube. Cork the test tube and label with the depth and location of the sample. Repeat at different locations and depths for the best results, keeping your samples separate. Bring distilled water in sterile test tubes with you to the sample site to use as blanks. Open the blanks for approximately the same amount of time that it takes you to obtain your samples. This is your control. By comparing the control with your samples, you can determine if the organisms in your sample are from the lake or are contaminants.
Professional Samplers
- You may opt to purchase a professional bottle sampler if you desire to obtain samples at depth. You can obtain these samplers from Aquatic Research Instruments or Vernier. These samplers allow you to lower the apparatus to depth, gather your sample, then pull a trigger that shuts the sampler to be sure that your sample is from the location you desire.
Sampling Techniques
- Professional bottle samplers are designed to be used from a boat. When you arrive at the location you wish to obtain the sample, rinse the sampler three times with distilled water. Lower the sampler to the depth you desire and pull the trigger on the device. This will close the doors, trapping your sample inside. Raise the sampler and transfer your sample to sterile test tubes. Bring the control test tubes with you on the boat and open them to the air while you are collecting your sample, as described in Section 2.

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