Topics  > Biology > Botany

Effect of water hardness on seed germinationFeatured science projectScience project video

popular science fair projects
Complexity level:
Project cost ($):
Time required:
1 day to prepare, 5 days for the science project experiment
Material availability:
Easily found
Safety concerns:

Basic safety requirements


This science fair project was conducted to ascertain if the hardness of water used on seeds will affect their germination. The science project experiment involved blackeyed Susan seeds that were made to germinate by watering with hard water, tap water and soft water.


Watering plants with soft water will help seeds germinate more quickly


Water and plant growth

Seeds need water, oxygen and the correct temperature before they can start to germinate and grow. After the seeds have germinated, they will also require light and carbon dioxide for photosynthesis. Plants will normally die if they are deprived of water and oxygen. The amount of water supplied to the plant or seed is also important. Too much water will cause the roots to be covered with water and deprive them of oxygen. This can cause the root to rot and kill the plant.

The water that we obtain from the tap or other sources is normally not pure. There will be some minerals or divalent salts in the water. The most common is calcium, magnesium and iron. The amount of calcium and magnesium present in the water will determine the hardness of the water.

The hardness of the water can be reduced by using water softeners. Water softeners help to reduce the amount of calcium and magnesium that is dissolved in the water. Sodium carbonate is an example of a water softener that is commonly used. Water softening takes place by ion exchange where the sodium ions and calcium, or magnesium ions, will "exchange" places.

Scientific Terms

Germinate, photosynthesis, divalent salt, water hardness, water softeners, ion exchange


The materials required for this science fair project:
- 1 packet of black-eyed Susan seeds (minimum 60 seeds)
- 3 large beakers
- 3 balls of cotton, enough to fill the above beaker
- 10ml of water softener
- 5 mg of calcium
- tap water
- 1 measuring cylinder
- 1 black marker pen


1. For this science fair project, the independent variable is the hardness of the water – hard water, tap water, soft water. The dependent variable is the number of seeds that germinate. This is determined by observing the seeds every day. The constants (control variables) are the environment the plants are kept in (temperature, humidity, light, etc), the type of plant used, the amount of water used and the size of the container.

2. The 3 beakers are labeled as “Hard”, “Tap” and “Soft”. One ball of cotton is placed inside each of the beakers. The packet of black-eyed Susan seeds is opened and 20 seeds are placed on the cotton in each of the beakers. The seeds are arranged so that they are at least 5mm away from each another.

3. Using the measuring cylinder, 200ml of tap water is poured into the beaker labeled “Tap”.

4. The 5 mg of Calcium is mixed with 200ml of tap water and poured into the beaker labeled “Hard”.

5. 10 ml of water softener is mixed with 200ml  of tap water and poured into the beaker labeled “Soft”.

6. The number of seeds germinating in the 3 beakers is observed for the next 5 days and recorded in the table given below.



It is observed that the rate of seed germination is almost the same for all types of water used.

Type of water used

Number of seeds germinating over 5 days

Day 1

Day 2

Day 3

Day 4

Day 5

Hard water






Tap water






Soft water







The chart below represents the results of our science project.

Water hardness and seed germination science project


The hypothesis that watering plants with soft water will help seeds germinate more quickly, is proven to be false.

Water hardness is however, very important for the survival of fish and other aquatic life. The calcium diluted in the water can be absorbed by the fish for bone formation, metabolism and blood clots. The presence of calcium or other minerals in the water also helps in preventing the loss of important minerals like sodium or potassium from the fish’s body fluids.

Also consider

This science fair project may be repeated, this time, with different types of plants like marigold or radish seeds?

Modify the science project experiment, using different environments like placing them under the sun, in a shaded area or indoors.


How to water plants -

Water softening -

Understanding water hardness -