Which Addition to Hard Water would Reduce its Conductivity, Washing Soda or Rain Water?

based on 2 ratings
Author: Michael Calhoun
Physical science  
Grade Level

Middle School (grades 6 -8)  

Difficulty of Project


Cost (Approximate Cost)
About $20.00  
Safety Issues

Hard water is not a health hazard, but handling hard water over a prolonged period of time can produce dry skin also, hard water will aggravate or inflame any conditions already present with the skin including psoriasis, or any type of rash or hives. The investigator should wear disposable plastic or rubber gloves when handling the hard water and the washing soda. 

The investigator should not ingest the substances used or drink the liquids associated with this activity. The supervising adult should discuss the warnings and safety information with the child or children before commencing the activity. 

Material Availability

The materials required for this project are readily available. 

Approximate Time Required to Complete the Project

Two hours after rain water has been collected. 


Hard water refers to the presence of dissolved ions, mainly of calcium Ca2+ and magnesium Mg2+ which are acquired through contact with rocks such as limestone and dolomite which contain calcium and magnesium. The research aspect of this science fair project is to use a conductivity device to determine which actions will reduce the ionic concentration of hard water better, the addition of washing soda or rain water. 

This science fair project focuses on the use a conductivity device that will enable the investigator to determine the ionic concentrations of hard water before and after it has been treated chemically and by a physical process. The investigator will first measure the conductivity of a test sample of hard water, than this sample will be equally divided and placed in two containers. Washing soda will be added to one cup and the other will be allowed to collect rain water. After a pre-set time the conductivity of the samples will be measured and recorded in a data table, from which a graph displaying the result will be plotted. 

Materials and Equipment /Ingredients

A conductivity device, a package of clear plastic cups, plastic spoons, dish washing detergent, distilled water, hard water either from the kitchen faucet or a nearby stream flowing through an area with high limestone rock deposits.

With the exception of the conductivity device all of the materials can be purchased from the local supermarket or major retail (Wal-Mart, Target, Dollar General, etc) discount department store. The Tri-fold display board can be purchased from an art & craft store.  

A conductivity device can be purchased from the following online venders: Science in A Bag Conductivity Circuit Board Indicator” retails for about $16.00 and includes free shipping. ScienceKit Inc “Audio/Visual Conductivity Indicator” Catalog # WW45354M50 retails for about $42.00 and sometimes comes with free shipping and handling.  

Add your own comment