Water quality can be important for the health of your plants. Depending on where your water comes from, it likely contains many natural salts that are found in regular tap water. These salts give water their taste, and can also affect how much room there is left in the water for fertilizers. There are many ways to measure these salts, and in my opinion the easiest and most universal is electroconductivity. Electroconductivity, or E.C. is the ability of water to conduct electricity. On its own distilled water will actually conduct no electricity. The salts and ions in the water is what allows the solution to conduct. This is what allows us to estimate the strength of a nutrient solution by measuring the electroconductivity of the water. If the E.C. of the water before you add nutrients is above 0.3 then there is not as much room available for fertilizers as a solution that has an ec of 0.0.
If your starting water has a high E.C. you may want to consider getting your water from another source, or moving to an reverse osmosis filter. A reverse osmosis filters, or R.O. filters works by stripping salts from the water by forcing it through a membrane. A drainline containing salty water is then wasted, and a line containing the clean water will be collected in a tank. If your beginning water is very salty this will cause your filter to produce excess waste water. These types of filters work very slowly, smaller units will make 100 to 200 gallons of water per day. This could mean a garden that uses more than what the filter can produce will need to store extra water in a tank.
Salty water can be successfully used to grow plants, but it can be challenging and more difficult to identify problems as they occur. Tap water is nice because it is so easy to use, but the quality of tap water can change over the course of the year depending where you live. In Ohio the water companies may use different additives in the winter than in the summer. This can cause some gardens to achieve different results at different times of the year just because the water company makes adjustments. In some areas you can contact the water department about the additives used. R.O. water is nice because it created a zero salt standard water that is consistent every time. It is important to regularly change your filters to maintain maximum effectiveness.
Some people prefer not to use R.O. water because of the pH fluctuations. These fluctuations people experience with R.O. can usually be fixed by adding a small amount of tap water back in, or a small amount of pH stabilizer