Some useful information about this can be found in this article from the Government of Western Australia. According to this article for a healthy person the salt content becomes a concern if the water tastes salty.
However for those who have to keep to a low salt diet it gets more difficult.
"...the following people should be aware of the level of sodium (salt) in drinking water when the level is greater than 20 mg/L:
- Persons who are monitoring their salt intake for high blood pressure
- Persons with cardiovascular or heart disease
- Persons with kidney problems or
- Persons on low sodium diets."
From what I have been told measuring the salt content is not easy and this would at present be likely to mean sending samples outside Guyana.
On a quick check most bottled water gave no salt content information on the label. One brand gave a salt content of 20 mg/L and one other stated that the water contained no salt. The GWI website did not provide such information either.
The salt content of our local water can be adversely affected by dry conditions and by salt water intrusion. As we experience climate change this will need to be monitored more closely.