Hello and thanks for the question,

Is your tap water from a public water company or do you have your own private well/spring at home? Public water suppliers are required to regularly test the water that is delivered to your home and you can get a copy of those tests results as part of their annual consumer confidence report. You should call the phone number on your bill and ask for that if you have concerns about what might be in your water. However, once the water enters your plumbing it may change based on the type of plumbing you have or any treatment systems you use like water softeners, etc.

If you have your own water supply like a well or spring, you will have to have that tested on your own. There are a number of DEP certified laboratories across the state that you could use for that. You can find guidance on that here: http://extension.psu.edu/natural-resources/water/drinking-water/water-testing/testing

As far as what things in your water to look for that could be effecting your plants, you might look to find out the pH (how acidic your water is) first. Plants can only tolerate certain pH levels and this could be impacting your houseplants.

Another thing to look for is the hardness of your water. Very hard water is full of calcium and magnesium. Those minerals are good for plants but not really in the form they take in your water. They can block the normal functions of plants.

Water softeners will remove the excess calcium and magnesium, but they replace it with salts which are equally harmful to houseplants in high quantities. If you are currently using a softener, you might try watering your plants using water that has bypassed your treatment system. The hardness may not be as harmful depending on the level.

You may be able to skip purchasing bottled water and just use collected rain water as a substitute to your tap water if you are unable to identify the problem or change it.

Note that pH and hardness are not human health issues in your drinking water. 

Best of luck!