All water contains some sodium, whether tap, filtered, or bottled, sparkling or still.....the only way to check how much is to read the bottle-label or by phoning your water supplier.
Some years ago, a CD instruction booklet recommended only limited quantities of sparkling water - but this is because some people find that the bubbles can cause ructions from one end or t'other!
I'm happily addicted to Highland Spring sparkling, but over the years, it has varied from 4.5 to (today) 9.4 mg/L - presumably because it's a natural product from various different springs. It's still very low, compared with other brands - last time I looked, Buxton Sparkling was 116 mg/L.....which doesn't matter if you're only drinking a bit of it, but very important if you get through gallons and have high blood pressure, for example, or need a low-sodium diet.
So - another example of that all-important lesson - read the labels when you're shopping! (And allow another hour or two!)