KALIA HARRIS

she/her | age 11 | Ottawa, ON

Turnbull School Grade 6 Science Fair Winner

INTRODUCTION

Greywater is gently used water from your bathroom sinks, showers, tubs, and washing machines. It is water that has not encountered feces, either from the toilet or from washing diapers (Greywater Action, 2022). Greywater may contain traces of dirt, food, grease, hair, and certain household cleaning products. While greywater may look “dirty,” it is a safe and even beneficial source of irrigation water in a yard. Even if greywater is released into rivers, lakes, or estuaries, its nutrients become pollutants, but to plants, they are valuable fertilizer.

Aside from the obvious benefits of saving water (and money on your water bill), reusing your greywater keeps it out of the sewer or septic system, decreasing the chance that it will pollute local water. Overall, reusing greywater for irrigation reconnects urban residents and our backyard gardens to the natural water cycle (Greywater Action, 2022).

PURPOSE & HYPOTHESIS

The purpose of my experiment is to help conserve, recycle, and reduce water waste by reusing “grey water.” Greywater is water that has been recycled from bathing, shower water or snow. I will use this “grey water” to try and grow plants. My hypothesis for this experiment is that the cleanest “grey” water will grow the best plants. I predict that the water with the least bacteria should be the healthiest for the plants. I made this prediction based on the findings that the healthiest water for human consumption is water that has been filtered and has the least bacteria.

MATERIALS & METHODS

Materials

Soil

Jacob’s Cattle Beans
Mobile Klean UV sanitizing wand
SEAWEED SOLUTION LABORATORIES Nutrient Agar Kit – 10 pack
Shower water with soap
Bath water with soap
Dirty snow from roadside
Clean snow from backyard
Distilled water
Old Bottled water
LUCIANO HOUSEWARES food storage container x12
3.1 L YOUNG EVER mini-indoor pots 10 pack x3
3-inch MODERN HOUSEWARE white spray bottles x13
P-TOUCH manual label maker
MCKENZIE grow light (Deluxe Growing System) x2
LINK PRODUCTS all-purpose tray - 33 x 56 cm
Plant label markers waterproof (2.4 x 4 in)
Distilled water
30 cm tape measure
CANADIAN TIRE green pots (0.46 L)

Methods

Use the large storage containers (3.1 L) to collect water samples from different sources: bath water (after bathing), shower water (after showering), snow from the backyard, dirty snow from the roadside, and bottled water that has been left out several days. You will also need a control group. Fill one large storage container with distilled water. You should have 6 containers full of water at this point.
Gather the remaining 6 storage containers and pour half of the water from each source into a new container. Try and evenly split the water into 2 equal groups.
Use the label maker machine to make the following labels, you will need to make 4 labels for each water source:
a. Shower Water Bath
b. Water Snow Clean
c. Snow Dirty
d. Old Bottled Water
e. Control Shower (UV)
f. Bath (UV)
g. Snow Clean (UV)
h. Snow Dirty (UV)
i. Old Bottled Water Control (UV)
Label all containers, Petri dishes, bottles, small pots, and big pots with each label.
Take UV light and sanitize each container of water that is marked UV (DO NOT SANITIZE THE ONES THAT DO NOT HAVE UV marked on them). Sanitize as follows:
a. Hold UV light at the top of the water for 20 seconds.
b. Hold UV light at each side of the water container for 20 seconds each.
c. Repeat each sanitization three times.
d. Make sure to use small coloured dot stickers to keep track of how many times you have sanitized the containers.
Transfer different water sources to the spray bottles, making sure to follow the labels.
Count out 12 Petri dishes and label them.
Make nutrient agar for Petri dish.
Spray each Petri dish with the different water sources. Set all Petri dishes aside.
Gather 24 Jacob’s Cattle Beans.
Count 12 small white pots and saucers for plants.
Set up pots on black tray as seen in Figure 1 below.
Label each pot with each different type of water source.
Take bags of soil and place in a large bucket.
Moisten soil by spraying warm control water (distilled water) into soil while mixing it with your hands.
Don’t drown the soil, make sure it is only moist.
Fill pots with soil up to the small line inside the pot.
Plant 2 beans in each pot 2 inches apart from each other, push beans 2 cm into the soil, cover beans back up and compress soil.
Water each pot with the appropriate spray bottle, make sure the soil is moist and not too damp.
Water each plant with APPROXIMATELY the same amount of water.
Set up two UV growing lamps. Set up tray under UV plant growing lights near a window. turn growing lamps on.
Place two lights above each row of plants.
Rotate the tray back and forth each day so each row of plant gets the same amount of sunlight.
Set up a chart to record observations and take pictures daily.
Measure the height and width of each plant daily. Measure the bacterial growth on the Petri dish daily as well.
Describe characteristics of each plant ex: healthy, dying, etc.

**Figure 1: Set up of pots.** ROW 1: BATH – SHOWER - SNOW DIRTY - SNOW CLEAN - OLD BOTTLED WATER - CONTROL. ROW 2: BATH UV – SHOWER UV - SNOW DIRTY UV - SNOW CLEAN UV - OLD BOTTLED WATER UV - CONTROL UV.

RESULTS

Many things have happened whilst growing these beans. To start, the UV light is affecting the growth rate of the plants. The plants that were watered with UV light treated water have been healthier, bigger, and faster growing (Tables 1 and 3). The plants that were not treated with the UV light did not grow as well (Tables 2 and 4). Even though some took a while, every single plant that had sanitized water grew. However, the plants with the untreated water took a bit longer and weren’t as healthy. The plants grown with dirty snow water were visibly different. One of the two plant’s leaves was dark, wrinkly, and deformed. The other plant not treated with UV light didn’t even grow. As seen in Figure 2, the plant watered with old, bottled water was the healthiest, and one of the biggest and brightest plants. As an observation for the petri dishes, it was really clear that the UV reduced the amount of bacteria in the water source (Figure 3). There was a noticeable difference in the amount of bacteria after 2 weeks between the UV treated water and the non-UV treated water. Figure 4 shows the layout and growth of the plants over the 2-week experiment period.

**Table 1**: Height, width, and description of 6 different plants treated with UV light over the course of a week. The two plants treated with the “old, bottled UV water” were most successful as they were the first to grow and most healthy.

**Table 2**: Height, width, and description of 6 different plants treated without UV light over the course of a week. Overall, the plants that were not treated with UV light did not grow well.

**Table 3**: Height, width, and description of 6 different plants treated with UV light after 2 weeks. The two plants treated with the “old, bottled UV water”, bath UV, and shower UV were most successful as they grew to the largest height and width.

**Table 4**: Height, width, and description of 6 different plants treated without UV light over the course of 2 weeks. Overall, the plants that were not treated with UV light did not grow as well, they were slow to start. However, eventually the plants water with “Old bottled water” and bath water grew well.

**Figure 2**: Final height of all plants after 14 days (2 weeks).

**Figure 3**: The bacterial growth shown in Petri dishes with different watering treatments.

**Figure 4**: The growth of each plant over 14 days, comparing Day 1 to Day 14

DISCUSSION

An unexpected result was that plants with soapy water grew extremely well and quickly. I suspected that the soap in the water may have helped kill off germs in the water helping the plants grow. I also found that the UV light does actually reduce bacteria and likely sanitized the water in my experiment. One surprising result was that the plant grown with the control water didn’t grow very much. For the control water, I used water that was treated with reverse osmosis, a special way to clean and sanitize water. I had predicted that plants watered with this water source would grow really well. Another thing that shocked me was how the old bottled water that had bacteria from people’s mouths on it actually helped grow the plant better than control water. Also, the plants watered with CLEAN snow water had taken quite a while to grow. However, I wonder if this could have been the result of a defective bean or improper watering methods.

Gardens can come alive with the sheer volume of Greywater alone as it contains a wealth of micro-nutrients. One class of micronutrients found in Greywater is organic matter such as skin cells and phosphorus, which is found in most soaps and commonly used as fertilizer (Higgins, 2023). This would explain why the plants watered with “Old bottled” water grew so well. Research done by Younis et al. (2019) has also shown there was an inactivation of plant pathogens in irrigation water runoff when using a UV disinfection system which helped plants grow. This would also help explain why the plants watered with UV treated water also fared much better. A study done by Shallcross in 2023 showed that reverse osmosis is good for plants because it doesn’t contain any harmful chemicals, heavy metals or other impurities found in normal tap water; however, it lacks essential minerals which are beneficial to plants. This would help explain why I found that the “Old Bottled” water plants actually outperformed the plants irrigated with the reverse osmosis treated water which I used in my control group.

I expected the dirty snow water to grow the worst plants and they barely grew. The plant grown with dirty snow water (non-sanitized) had some sprouts in the soil and then stopped growing completely. The plant grown with the dirty snow water treated with the UV grew out of the soil but stopped growing after it reached around four centimetres. In the water, there was oil, dirt, and gas from cars which likely caused the plant to stop growing. This plant was unusually small and wrinkly and looked deformed.

A source of error for the experiment could have been from the water bottle sprays that were used. The sprays were not always consistent in strength, and some were less powerful. Another problem is that the bottle used for Dirty Snow water often got very clogged and I had to keep manually pouring it. This may have affected the growth of the plant significantly. Another source of error could be the amount of sunlight that the plants received. The plants were rotated to ensure that they had equal exposure to the window, however some days were sunnier than others. A UV light was used but the extra sunlight could have boosted the growth of some plants unfairly. Another possible error could have been from planting a stunted bean that just won’t grow no matter what.

The experiment could have been improved by ensuring that the strength of the spray triggers of the bottles were the same or as close as possible. I believe if I focused more on testing the presence of bacteria in the plant itself, the experiment would be more meaningful. I would like to know if the beans produced by the plant are suitable to eat. I also could have been more precise with the amount of water, sunlight, and the heat each plant gets. Finally, I would also have used more plants. I would have grown at least 3 plants for each water source to get more accurate results. By growing multiple plants at once, it would be similar to doing multiple trials of the experiment. In this way, I could confirm that my results were accurate.

My results are important because they give us more information on how we can reuse water safely. The experiment showed the benefits of using UV light to help sanitize water. According to Advanced Biotechnologies Inc (2021), “UV light has been used for sterilization and disinfection as early as the mid-20th century. With advancements in technology, and specifically in the UV bulbs themselves, their reliable long lifespan (thousands of hours) and smaller size (e.g., UV LED vs traditional UB bulbs) has broadened the field for where it can be used. You can find it being used to disinfect water, air, fruits, vegetables, surgical utensils, tablet computers, toys and a variety of surfaces”. My experiment showed you can use a very small handheld UV light to help clean water. Another study showed that: “Pollution in water not only harms plant growth but also allows plants to absorb dangerous chemicals from the water and pass them on to animals that rely on them for survival” (King, 2017). My experiment is helpful because it shows that “grey water” can be used to help grow plants and increase water sources for people to use. This is good for both the environment and for poorer countries who have limited water sources.

REFERENCES

Advanced Biotechnologies Inc (n.d.). Is UV Sterilization Eﬀective for Viruses and Bacteria? Retrieved September 24, 2023, from https://abionline.com/is-uv-sterilization-effective-for-viruses-and-bacteria/.
King, YaShekia. (2023, September 28). The Effects of Water Pollution on Plant Growth. sciencing.com. Retrieved from https://sciencing.com/the-effects-of-water-pollution-on-plant-growth-12423700.html
Greywater Action (n.d.). About Greywater Reuse. Retrieved September 24, 2023, from https://greywateraction.org/greywater-reuse/
Higgins, K. (2023). WATERING GARDENS WITH GREYWATER – PLANTS THAT LIKE GREYWATER. Retrieved September 24, 2023, from https://www.gwig.org/watering-gardens-with-greywater-plants-that-like-greywater/
Younis, B.A., Mahoney, L., Schweigkofler, W. et al. (2019). Inactivation of plant pathogens in irrigation water runoff using a novel UV disinfection system. Eur J Plant Pathol 153, 907–914 (2019). https://doi.org/10.1007/s10658-018-01608-8
Watson, S. K. (2018). Which Water Is Best For Health? Hint: Don't Discount The Tap. Retrieved September 24, 2023, from https://www.npr.org/sections/thesalt/2018/07/27/632393234/which-water-is-best-for-health-hint-dont-discount-the-tap npr.org

Reducing Water Waste: Reusing Grey Water