– Why do we need to use washing up liquid to clean dishes? Why would water alone not suffice?

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My dad and I are having a debate about the importance of using washing up liquid and I need your help!!

He proffers that water in itself is clean, so why can we not just use water to clean our plates etc.

He also gave an example of how we would likely feel cleaner after “trudging through the jungle”, if we had a wash in a big jungle waterfall without soap.

I showed him that his glasses come out looking cleaner (no water marks) when he washes them with washing up liquid to prove my point that it is important to use it.

But can anyone tell me the actual science behind why we should use it? Or is my dad right? 😂

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22 Answers

Anonymous 0 Comments

You can win this with a practical demo. Have him put some oil on his hands (olive oil, salad dressing, etc.) and try and rinse it off with just water. It will be nearly impossible, because oil and water don’t mix. Water alone can’t carry away oil because it can’t mix with it. If he gets the oil off at all it will take a long time and a ton of scrubbing.

Almost all food has at least some non-zero oil or fat level. When oil is on something it forms a layer that water alone physically can’t penetrate or remove.

What soap does is act as an “intermediate” substance that allows oil and water to mix, which allows the water to carry the oil away. Add some soap to his oily hands and let him try clearing them in water again. He will see for himself how much faster, easier, and more thorough the removal of oils/grease/fat is when there’s soap to let the water do its work.

And since removing oils/grease/fat is exactly what you’re doing when washing dishes, you need soap for that too.

Anonymous 0 Comments

You can win this with a practical demo. Have him put some oil on his hands (olive oil, salad dressing, etc.) and try and rinse it off with just water. It will be nearly impossible, because oil and water don’t mix. Water alone can’t carry away oil because it can’t mix with it. If he gets the oil off at all it will take a long time and a ton of scrubbing.

Almost all food has at least some non-zero oil or fat level. When oil is on something it forms a layer that water alone physically can’t penetrate or remove.

What soap does is act as an “intermediate” substance that allows oil and water to mix, which allows the water to carry the oil away. Add some soap to his oily hands and let him try clearing them in water again. He will see for himself how much faster, easier, and more thorough the removal of oils/grease/fat is when there’s soap to let the water do its work.

And since removing oils/grease/fat is exactly what you’re doing when washing dishes, you need soap for that too.

Anonymous 0 Comments

soap gets rid of fats and oils and things that won’t come off with water, and it gets rid of bacteria (should any bacteria be on your dishes in the first place)

Anonymous 0 Comments

soap gets rid of fats and oils and things that won’t come off with water, and it gets rid of bacteria (should any bacteria be on your dishes in the first place)

Anonymous 0 Comments

Rub some butter on a Tupperware container and tell him to try to clean it with just cold water. It will continue to feel greasy no matter what you do. You might be able to get it clean eventually with extremely high temperature water, but using detergent will make it stop feeling greasy a lot faster.

It’s easiest to demonstrate this with plastic because it holds onto grease, but really this applies to anything. Detergents break grease up into tiny little droplets, stop those droplets from merging together, and suspend them in the water so they can be washed away. The majority of food residue that won’t just rinse off in water is greasy. Dish liquid often has other ingredients besides just detergents that can help with messes other than grease, but really it is mostly just the grease-cutting that is doing the heavy lifting.

Anonymous 0 Comments

Rub some butter on a Tupperware container and tell him to try to clean it with just cold water. It will continue to feel greasy no matter what you do. You might be able to get it clean eventually with extremely high temperature water, but using detergent will make it stop feeling greasy a lot faster.

It’s easiest to demonstrate this with plastic because it holds onto grease, but really this applies to anything. Detergents break grease up into tiny little droplets, stop those droplets from merging together, and suspend them in the water so they can be washed away. The majority of food residue that won’t just rinse off in water is greasy. Dish liquid often has other ingredients besides just detergents that can help with messes other than grease, but really it is mostly just the grease-cutting that is doing the heavy lifting.

Anonymous 0 Comments

Oily substances repel water. Soap bridges the gap between oil and water allowing the water to wash away the oils that would normally repel it.

Water alone cannot clean oil off of a surface entirely.

Then you get into bacteria and microorganisms that not only aren’t washed away by water, but thrive in it and require it to survive and multiply. Soap is also often a disinfectant, killing those bacteria/microorganisms outright while also also clinging to them like it does oils so water can wash it away.

Anonymous 0 Comments

Oily substances repel water. Soap bridges the gap between oil and water allowing the water to wash away the oils that would normally repel it.

Water alone cannot clean oil off of a surface entirely.

Then you get into bacteria and microorganisms that not only aren’t washed away by water, but thrive in it and require it to survive and multiply. Soap is also often a disinfectant, killing those bacteria/microorganisms outright while also also clinging to them like it does oils so water can wash it away.

Anonymous 0 Comments

Well your dad would be right, if he had used water that’s hot enough to kill all the bacteria, which would be just slightly below boiling. But I doubt he does that.

So you’d need dish soap, which doesn’t kill the bacteria but it will lift them off the surface so that they can be washed away.

Otherwise you’d have a lot of bacteria, even potentially dangerous ones like salmonella festering on your plates.

Anonymous 0 Comments

Well your dad would be right, if he had used water that’s hot enough to kill all the bacteria, which would be just slightly below boiling. But I doubt he does that.

So you’d need dish soap, which doesn’t kill the bacteria but it will lift them off the surface so that they can be washed away.

Otherwise you’d have a lot of bacteria, even potentially dangerous ones like salmonella festering on your plates.