In reality there is no one water that is healthiest although there are a few that are questionable.  The key thing is to have clean, safe drinking water.  Your specific needs, what is available and affordable will decide what is best for you. Let us look at each one.

Tap Water:

Tap water is municipal drinking water and is piped into homes from a central water treatment facility. Depending on where you live, it might contain added fluoride. Water quality, purification method, and treatment process varies in different communities but they tend to include steps that add minerals and remove solids, filter, and disinfect the water.

Reverse Osmosis (RO) Water:

This water has passed through a semipermeable membrane to remove minerals, molecules, and other impurities in the water. Unfortunately, this process can remove essential minerals such as magnesium and calcium.  It is for this reason that some researchers are concerned about negative health effects of this water.

De-ionized (DI) Water:

This water treated water has “ions” which are particles with a negative or positive electrical charge removed. That usually means all the dissolved mineral salts.  This treatment creates a more controlled research environment in laboratories.  As with the RO treatment, some researchers are concerned about potential health risks associated with this water.

Alkaline Water:

Alkaline water has a higher pH level than regular drinking water.  Normal drinking water has a pH level of 7 while alkaline water has a pH of 8 or 9.  There is no scientific evidence that alkaline water provides health benefits including claims of longevity.   Natural alkaline water such as spring water is safe because it contains natural minerals.

Mineral or Sparkling Water:

Mineral water comes from a natural source and can be either flat of natural sparkling.  This type of water comes from an underground source and contains at least 250 parts per million of total dissolved solids.  Sparkling water is fizzy thanks to a man made carbonation process, which can add a slight bitterness to the water.

Spring Water:

Spring water comes from an underground formation from which water flows naturally to the surface. Natural spring water is safe to drink and contains only minerals that were naturally present in the spring including calcium, magnesium, and a trace of sodium.

Well Water:

Well water comes from an aquifer deep in the ground. Well water needs to be tested regularly to ensure its level of purity and that no contamination has entered the water source. Well water will have various levels of pH depending on the type of rocks and geographic features close by

Drinking enough water is critical to your health.  How much you should drink varies for everyone.  The MayoClinic claims that healthy adults should drink about 7 – 11 (12 ounce) glasses of water each day.  This includes water from the foods you eat and other beverages such as tea and coffee.  However, other factors have an influence of how much you should drink including how much you exercise, the weather, and if you are pregnant.  If you are unsure about your diet or drinking habits, best to talk to your doctor.

https://www.nutrisense.io/blog/types-of-drinking-water