Have you ever seen white spots forming on bathroom or kitchen faucets? They come from minerals dissolved in the tap water. When the water evaporates, the minerals are left behind. We also speak of lime stains as well as calciferous or hard water. Water with little lime is called soft water. So-called distilled water contains no lime or other minerals at all.
Hard water, soft water – does it matter?
Lime stains are only one side effect of hard water. Water hardness also affects every washing process – whether it's doing laundry, washing dishes or washing hair. This is because the lime in the water reacts with the cleansing substances, the surfactants. The effects can also be seen in the foam: the harder the water, the less foam.
We investigate this with a simple experiment.
You will need
- Empty plastic bottles
- Tap water
- Distilled water*
- Measuring cup
- Bottled water with high calcium content
- A teaspoonful of dishwashing detergent or shampoo
* from the supermarket
Let’s get started!
1. Preparation
Pour 100 ml of tap water into an empty 1 l plastic bottle. Mark the liquid level (100 ml) with a marker. Add another 100 ml of water and mark the liquid level (200 ml). Repeat the steps until you have marked 1000 ml (= 1 l). Then prepare the second plastic bottle in the same way.
2. Water samples
Measure 200 ml of distilled water in a measuring cup and pour it into the first bottle. Then measure 200 ml of the high-calcium water and pour it into the second bottle. Finally, add half a teaspoon of dishwashing detergent or shampoo to each bottle. Then firmly close both bottles.
3. Shake and compare
Now shake both bottles vigorously for half a minute. When you are done, place them side by side and compare: Which one developed more foam? Make a note of which mark the foam reaches in the two water samples.
Finally, you can repeat the experiment with tap water. Compare the foam level of your tap water with the other two types of water. Is your tap water hard (little foam) or soft (a lot of foam)?
