The best water for the volcano shrimp is aquarium sea salt mixed with pure distilled water. The reason is because there are chemicals and impurities in our tap water.
Chemicals are added into our drinking water to kill bacteria and pathogen.
The water is pumped come from our water company all the way to our house through various water pipes. These pipes introduce dissolved metal and impurities into the tap water.
Alternatively, you can always collect clean rain water. But before you do that, let it rain for about 15 mins or longer to wash away any surface contamination.
The rain water collected will be much cleaner.