I believe they are saying raw water (untreated) is 50ppm, but treatment reduces it to less than 1ppm.
But....I would call them to be sure.
In the US, 10ppm is the maximum amount of nitrate allowed in treated water for human consumption, because anything over 10ppm is dangerous for very young children (causes methemoglobinemia(blue baby syndrome)).
No legitimate water treatment facility would surpass the MCL.
And if for some reason your tap water had a nitrate concentration over 10ppm, there would be a media blitz warning that any children under the age of 2 years, should only drink bottled water.