While there is no "best" water, any naturally sourced water like Spring that you enjoy will be the best one. 

Tap water in the US is regulated by the EPA and in most cases is safe to drink. If you are still concerned, you can check the EWG Tap Water Database for your area.

While wild water should not be consumed, there are safe places to drink natural spring water for free.  Check out findaspring.org to see if there is a spring in your area.

This is a real problem but the truth is, is that bottled water uses much less water to produce than soda, wine, or beer. Also, avoid purified water which takes up over 50% of the plastic in the water section. Buying water in glass, tetra, or aluminum will always be a greener choice than PET. 

Water needs minerals to keep you hydrated.  While many households utilize a filter for their water to protect their skin and hair, there is no reason to buy purified water at the store. It is just filtered tap water.

The FDA regulates any naturally occurring bottled water sold in stores in the US and it is safe to drink. Some waters with a very high TDS of over 2000mg/L can be like a natural energy drink for some, but those prone to kidney stones and hypertension should take caution and ask their doctor before consuming. The "bad" (red light) readings on TDS meters are meant for tap water. A reading over 500ml/L in tap water could mean the presence of contaminants. 

DC, parts of Maryland, Virginia, USA

There are a few schools, but most are outside the US. Fine Water Academy is an online school that hosts both US and international students.