How to make artificial sea water My 7th grader is embarking on a long-term science project and I'm on tap to "help." He is showing a strong interest into finding ways to get drinking water to the masses. His idea is that we need to find inexpensive and efficient desalination processes. So, we are exploring current desalination processes to see what makes it "expensive" and "inefficient."

However, we live in the Rocky Mountains and don't have access to proper sea water. We started to explore simply adding salt to tap water and researching how much. Then, we discovered "Artificial Sea Water" or "ASW" is a common creation in science. Because sea water contains more than just salt. It contains chemicals like fluoride, strontium, boron, bromide, inorganic carbon, potassium, calcium, sulfate, magnesium, chlorine and of course, sodium. I am not a chemist, so this is starting to look daunting.

So, here are my questions to counsel my son:


To experiment with desalination, is adding salt to tap water
sufficient or do we need to investigate finding official ASW?
How do we test the salinity of water? Do I really need to invest
hundreds of dollars on a salinity meter?
If you look at the (average) composition of seawater:

       

you will find that NaCl is the main solute of this complex solution. Its concentration is 10 times higher than that of the next constituents (magnesium and sulfate). So, it seems to me like a simple NaCl solution is a good approximation for your experiments.

Regarding testing salinity of water, I don't have a definite answer on that, I do have two suggestions to offer:


Measure salinity by electric conductance of the solution, e.g. by making a simple conductometer and testing it with solutions of known concentration of salt.
Measure salinity by the quantity of salt (solid residue) once all water is evaporated. You can speed the evaporation by heating up.