Kitchen Sink Experiments

What is the best way to clean and disinfect the kitchen sink? 

Answer: At night or after handling raw meat, I scrub out my sink with a washcloth or scratch pad and then retire that item to the laundry. Then I spray the sink all over with a ton 3% hydrogen peroxide to fully cover the sink basins. Then I get a clean cloth or paper towel to wipe around the countertop at the edge of the sink or the 3% hydrogen peroxide will fade the countertop. Let the 3% hydrogen peroxide sit in the sink overnight. I recommend wearing gloves when using hydrogen peroxide.

Doesn't just washing the sink with soap, water, and a washcloth remove germs? 

Answer: Not very well.

Most of us have assumed that we don't really need cleaners to KILL germs. We can just wash them off with soap and water, right? This is a picture of my mother washing my kitchen sink. She loves to scrub out sinks and does it whenever she visits any of her children. You can always count on my mom to do the dishes, wipe up, and scrub out the sink whenever she visits. She can't cook, but she sure can clean up! She doesn't use any cleaning "chemicals". She just used Dawn dish soap and a cotton washcloth. But how well does that work? If you would like to know who I am, please read my About the Scientist page. 

Experiment Details

Here I set out to determine if I could remove most of the bacteria by just washing the kitchen sink really well with soap and water. For these experiments, I tested my kitchen sink and my neighbors' sinks. My sink usually didn't have enough bacteria to start with to get good results because I clean it too often. A sink needs to not be cleaned for a week before I can do an experiment in it. Luckily, my neighbors don't seem to sanitize their kitchen sinks very often and don't mind me doing experiments in them. First, I rinse the sink with warm water to remove food debris. All of the sinks LOOKED clean to start. Then, I swabbed the dirty sink and rubbed the swab onto an agar plate. That plate would be the dirty control.

Then I put some blue Dawn dish soap onto a cotton washcloth (wet with warm water) and washed one half of the sink for 2 minutes.  

I really did a thorough job. I doubt many people would normally wash this hard for this long. 

Then I rinsed the sink with warm water for about 30 seconds. I did not use hot water because I wanted to test how well the washing removed germs, not how well the hot water would kill them. I can do that another time. 

Next I swabbed the cleaned sink and rubbed the swab onto an agar plate. (I did not dry the sink.) 

Then I sprayed 30-40 sprays of 3 percent hydrogen peroxide onto the other side of the sink, let it sit for 5 minutes, swabbed that side, and rubbed the swab onto an agar plate. I do not wipe or wash when I use hydrogen peroxide. I just spray it on, let it sit, and then swab it. I realize that is a lot of hydrogen peroxide, but it takes that many sprays to completely cover the sink since I don't wipe it or spread it around at all. If I miss a spot, that will mean live bacteria on the agar plate. 

Understanding Agar Plates

In case you are new at looking at agar plates, let me explain. Agar is a Jello-like substance that bacteria and fungus like to grow on. The whitish/yellowish dots you see are colonies (or piles) of millions of bacteria. Some types of bacteria are not able to grow on these agar plates. Viruses can not grow on these agar plates. So, just because a plate looks clean, doesn't mean that no microorganisms whatsoever were present. We assume that a clean plate means that most bacteria were killed. However, there is the possibility that the cleaning product just stopped the bacteria from growing as opposed to actually killing it. 

RESULTS

Here are the results when I tested my neighbor's sinks. 

Here are the results when my mom cleaned my sink. She only scrubbed for 1 minute, though. 

As you can see, kitchen sinks are generally pretty germy and it is a lot harder than I thought to wash the germs off of the sink. Just understand that your sink is germy and don't eat out of the kitchen sink or prepare fresh food in it. Don't wash lettuce directly in your kitchen sink or eat a strawberry that fell into your sink. These experiments seem to show that 3% hydrogen peroxide works perfectly at killing germs in the sink. However, for these experiments, I did not rinse the 3% hydrogen peroxide down the drain before I swabbed. Therefore, the 3% hydrogen peroxide was picked up on the swab with the bacteria and incubated with it on the agar plate. So, I don't know if the 3% hydrogen peroxide killed the germs in 5 minutes or 5 hours. I did more sink tests with 3% hydrogen peroxide to figure this out. Keep reading to see those. 

Comparing washing the sink with blue Dawn to washing with just a wet washcloth. 

After the previous experiments where it appeared that washing with blue Dawn did not remove much bacteria, I wanted to compare washing with blue Dawn to washing with just a wet cotton washcloth. For these experiments, I used identical 100% cotton washcloths (Target Threshold brand which I love). The cloths were wet with tap water. One cloth had 1 teaspoon of blue Dawn on it. 

I swabbed each side of the sink separately so there were 2 dirty controls. 

Then I washed one side with the washcloth with blue Dawn for 2 minutes. (That is much longer than anyone would normally wash their sink.) 

Then I rinsed the sink for about 20 seconds with warm water. 

Then I swabbed the "clean" sink and rubbed the swab onto an agar plate. 

Then I washed the other side of the sink for 2 minutes with just the wet cloth with no soap at all. I rinsed it for about 20 seconds with warm water and swabbed that side. The plates were incubated for about 48 hours in my warm incubator.

Results

I was stunned that sometimes my washcloth with just water sink turned out cleaner than the sink I washed with Dawn!  I repeated the experiments several times and that didn't always happen. Sometimes the cloth with water and the cloth with blue Dawn did about the same.  

How could the washcloth with just water do about as good or better than a washcloth with blue Dawn? I even swabbed my blue Dawn itself to make sure it wasn't growing bacteria. It wasn't. 

My best GUESS as to why the washcloth with water removed bacteria better than the washcloth with Dawn is FRICTION. There was a lot more friction generated when I washed the sink with just the washcloth and water. The bubbly Dawn acts as a lubricant making washing out the sink easier with less friction. I repeated the experiments pressing as hard as I possibly could with the washcloth and Dawn combination to increase the friction. 

When I pressed super hard, the washcloth with blue Dawn did slightly better or about the same as the washcloth with just water. 

Will 3% Hydrogen Peroxide disinfect my kitchen sink? 

Answer: Yes but let it sit for at least 10 minutes or overnight. 

3% hydrogen peroxide does a great job producing a clean agar plate in my experiments. However, when I swab a kitchen sink that has hydrogen peroxide on it, the hydrogen peroxide gets picked up on the swab and is transferred to the plate. So, I don't know if the hydrogen peroxide kills the germs in 1 minute or 24 hours. So, I set out to test how long it takes for 3% hydrogen peroxide to kill germs in the kitchen sink. 

First, I swabbed both sides of a dirty sink and rubbed the swabs onto agar plates. Then I sprayed both sides with a ton of 3% hydrogen peroxide (about 40 sprays per side to completely cover the sink). After 5 minutes, I swabbed the right side of the sink and rubbed the swab onto an agar plate. This plate would have 3% hydrogen peroxide on it. Then I used the kitchen sink tap water/hose to thoroughly rinse off the left side of the sink. This would rinse the hydrogen peroxide off. Then I swabbed the left side and rubbed that swab onto an agar plate. The plates were incubated for 48 hours. 

Results

As you can see, the 5-minute swab from the side of the sink that still had hydrogen peroxide on it was all clean as usual. The side of the sink that was rinsed to remove the hydrogen peroxide, still had a lot of bacteria. From this we can conclude that 5 minutes is NOT long enough for the hydrogen peroxide to kill all the germs in the sink. I also took a swab of that neighbor's tap water and rubbed it onto an agar plate to make sure the water didn't contain bacteria. It did not. 

I repeated the experiment in another sink and left the hydrogen peroxide sit for 10 minutes. I swabbed the right side of the sink with the hydrogen peroxide still on it. I rinsed the hydrogen peroxide off the left side and then swabbed it. 

As you can see, there was still bacteria left in the sink after 10 minutes. However, it certainly seems like the 3% hydrogen peroxide is killing a lot of it in 10 minutes. I repeated the experiment again. This time I used 10% chlorine bleach on one side of the sink and 3% hydrogen peroxide on the other side of the sink. I used about 40 sprays on each side of the sink to fully cover it. They both sat for 10 minutes. Then I swabbed them both with the cleaner still on. Then I thoroughly rinsed them both and swabbed again. 

As you can see, the swabs where the cleaner was still on the sink were very clean as usual. The swabs from the sink that was rinsed after 10 minutes still had some germs. The 10% chlorine bleach did better than the 3% hydrogen peroxide. One reason that they both might not have done a perfect job is because the cleaner didn't really STAY on the sides of the sink. It dripped off right away. It does seem like 3% hydrogen peroxide does a whole lot of germ-killing in that first 10 minutes. 

I repeated the experiment on my sink. First I rinsed all the debris out of the sink and rubbed off any food particles that was stuck on. I swabbed my dirty sink and rubbed that swab onto an agar plate. Then I thoroughly sprayed the sink with 3% hydrogen peroxide. I used at least 40 sprays on each side and tried to cover everything. Then I let it sit all night for 9 hours. The sink was perfectly dry in the morning. In the morning, I thoroughly rinsed the sink and swabbed it again. 

As you can see, spraying the sink with 3% hydrogen peroxide and leaving it all night did a great job. So, if you want to disinfect your kitchen sink with 3% hydrogen peroxide, this is what I would do. At night, wipe out the sink with a washcloth or scratch pad, and then retire that cloth to the laundry. Then rinse out the sink with water. Then thoroughly spray it with 3% hydrogen peroxide. It is important to wipe around the edge of the sink with a clean cloth or paper towel so the hydrogen peroxide doesn't bleach the countertop. Then leave the hydrogen peroxide sit on the sink all night. I wear gloves when I use 3% hydrogen peroxide because it is hard on my skin and I can't guarantee it or anything else is perfectly safe for you. 

Disclaimer: I can't be 100% sure that they hydrogen peroxide or any product is actually KILLING the germs in these experiments as opposed to somehow preventing them from growing on the agar plate by some other means. 

When someone in the house is having diarrhea or vomiting, I recommend cleaning with a solution of 10% chlorine bleach in water or the Clorox Hydrogen Peroxide Spray

 and Clorox Hydrogen Peroxide Wipes because they have been shown to kill norovirus surrogates.