Bacteria Experiment on 5 Gallon Water Jug with Spout



People who either do not trust municipal water sources or simply do not like the taste or smell of their tap water often rely on water stores. These retail outlets offer purified drinking water typically filled in five gallon jugs with spout dispensers. 


Sometimes when filling up water containers, plastic bags are seen placed over the spigots. At home, there is a worry that fruit flies or other pests will come in contact with the spout. Pet owners worry that their pets may try to sip from the dispenser. Before using Spigcap™ one big worry was that the spouts were close to the floor of the car during transport. 

Do spouts on water jugs get dirty during transport, or at home? And if we use a Spigcap™, does it create a meaningful difference in cleanliness? This experiment will attempt to answer these questions qualitatively using bacteria culture plates.


Spouts on five gallon water jugs become ridden with bacteria during transport or while at home if left open to the elements.

Experiment Design:

A comparative test will be conducted in a real-world scenario using two five gallon water jugs over a weeklong experiment.

One will be left exposed and one will have a Spigcap™ attached. The water jugs will be transported in a car as usual to be filled. They will then alternate to be stored on a countertop for 3 days and stored in a water jug storage area for 3 days.

The Spigcap™ and spigots of each jug will first be washed with antibacterial soap and water for 30 seconds. One sample of each spigot will be taken with a swab and used as a control. After one week, another sample will be taken of each spigot and placed on Evviva bacterial agar plates. The plates will be incubated at 90 F for four days in sealed bags using a sous vide bath thermal regulator.
A few positive samples will also be taken of a sink drain and other household items to ensure the environmental conditions were suitable for bacteria growth.
At the conclusion of the experiment, the variation and number of bacterial colonies will be noted.
  • 2 Five gallon water jugs with spout
  • 1 Evivva bacteria agar test kit
  • 1 Spigcap™
  • 1 Large pot
  • 5 Zip-lock bags
  • 2 Pairs of sanitary gloves
  • 1 Sous-vide machine
  • 3 Household items


The specimens that come from exposed spouts will have more bacterial cultures. 


Experimental setup: 

The five gallon water jugs and Spigcap™ were first washed with soap and water for 30 seconds and dried with paper towels. The Evviva science kit contained sterile cotton swabs and distilled water for collecting samples. Samples were taken of the newly cleaned water jug spouts to establish two experimental controls.

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The water jugs were transported in two locations for added variability, first empty on the bed of a pickup truck, and then inside the truck once filled with water.  

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An additional source for contamination includes the moist conditions of the water filling area. 

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Here are the storage locations for the water jugs. As the pictures show, they alternated locations between a countertop and a storage area each for three days, and used under normal conditions.

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After the six days were complete, the samples were taken using the science kit materials. Additional samples were taken to observe bacteria that would commonly be present around the house. These samples included: the sink drain to establish a positive control, the TV remote, and a washed blue berry that was stored in the refrigerator. 

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Once all the samples were collected and labeled, they were each stored in zip lock bags and placed in the makeshift incubator, which consisted of a thermally regulated bath using a sous-vide machine set to 90 degrees fahrenheit for four days as recommended in the science kit instructions. The large pot was set in the kitchen with cling film over it to prevent the water from escaping as vapor, and then placed in the bathroom for four days.

5-gallon-water-jug-with-spout-bacteria-experiment-incubator1 5-gallon-water-jug-with-spout-bacteria-experiment-incubator2


The original control samples were not originally incubated in the sous-vide bath, rather, they were left in a room-temperature environment for the six days while the water jugs were stored. As expected, no bacteria is present where the cotton swab was rubbed. There was a small mold-like bacteria present in the [open air] plate for the spout with no cap, but not in a location where the swab was rubbed (where the visible streak marks were). It’s important to note that this bacteria growth is possible with the sensitive agar plates. As sterile as the conditions might be, there were other plates that were not usable and discarded because bacteria started to grow on them. The manufacturer recommends storing the plates in the refrigerator for this reason.

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After the sixth day, the control samples were placed in the incubator with the rest of the samples to determine if any other bacteria would grow on them under ideal conditions. As the pictures show, there is a small amount of spotted bacteria growth where the swab was rubbed for these agar plates which were incubated for 10 days. The bacteria growth suggests that despite the steps to ensure there was a sterile environment when collecting the samples, there was still a small amount of contamination originating anywhere from the water, paper towel used to dry the items, or the cotton swab itself.

5-gallon-water-jug-with-spout-bacteria-experiment-pre-test-no-cap2 5-gallon-water-jug-with-spout-bacteria-experiment-pre-test-spigcap3

The results of the household items including the positive test sample taken from the sink drain are shown below. The blueberry sample shows what could be some type of mold growth, which would be common for fruit. The controller sample shows a white and yellow spotted bacterial growth. The sink drain positive test sample shows densely spotted dark yellow bacteria which grew in streaks along the path on which the cotton swab was rubbed.

5-gallon-water-jug-with-spout-bacteria-experiment-blueberry2 5-gallon-water-jug-with-spout-bacteria-experiment-controller2 5-gallon-water-jug-with-spout-bacteria-experiment-post-test-sink-sample

Finally, the sample obtained from the spout covered by the Spigcap™ shows some light yellow spotted bacteria growth along the path of the cotton swab. The sample from the open air spout with no cap shows pink to red spotted bacteria growing along the cotton swab path.

5-gallon-water-jug-with-spout-bacteria-experiment-post-test-spigcap1 5-gallon-water-jug-with-spout-bacteria-experiment-post-test-no-cap2 

The samples were disposed of after pouring bleach over the bacteria cultures. 


Bacteria cultures were present in every agar plate that was incubated, highlighting the ubiquitousness of bacteria in daily life. While there is good and harmful bacteria, the exact type present in the plates remains a mystery, and without lab equipment to properly identify each type of bacteria that was present, the only option is a visual comparison among the samples collected. Please contact us if you have a science background and are able to identify any of the cultures present from the pictures provided. 

Interestingly, the most distinct bacteria colony is the pinkish red colony that grew from the sample collected on the spout which did not use a cap. With the limited information available, one possibility is that it is a Gram-negative bacteria, while the other colonies are Gram-positive.

Gram-negative bacteria colonies could be worse due to the presence of their outer membranes which protects them from antibiotics and other means to sterilize them. 

One possibility is that the pinkish red spotted bacteria may be Serratia Marcescens, but for now that remains inconclusive. 

Although the original prediction cannot be fully verified, the hypothesis could hold true. One important distinction among the samples is that all the samples except one look like what may be identified as common household bacteria - either white or yellowish spotted or moldy bacteria. The one sample that does not fit this category is the one which was exposed to the outer elements without a cap or other type of barrier. One possible conclusion is that the spout with no cap was exposed to a bacteria during the refill trip and possibly while being transported. It is important to note that the bacteria cultures grew under ideal conditions, and that bacteria may not proliferate under normal conditions.  

For anyone wishing to repeat this experiment, pay close consideration to the sanitary conditions of everything from the agar plates to the water and materials used to collect the samples, and please contact us to share the results.


Spigcap™ is made from durable food-grade silicone which is naturally BPA free, thermally stable, and has low chemical reactivity. It fits tightly around most standard spigots and maintains a barrier from the spout and fluids in the container against dusts, pests, and harmful bacteria. The user friendly design keeps spigots clean and prevents spillage when the container is tilted by clipping on to the stem. Wholesale pricing is also available. Patent Pending.

If you would like to stop worrying about contamination, order your Spigcap™ 3-pack.


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