Recently I decided to test the water at my apartment. Below are the results
Above is the water test for 20 liter jug. 49 ppm is considered safe drinking water.
Above is the water test for unfiltered tap water. 42 ppm is safe for drinking water. A surprise since the bottled water may just be tap water.
Above is the results for filtered water using a four filter system that includes reverse osmosis.
All results were based on the below chart.
Hence in my area of District 4 the water meets safe drinking standards. Unfortunately it does not measure the chemicals in the water. You still need a water filter but boiling and a Brita filter should be enough for most places in Saigon.