water table

I had my well water tested a while back and my main concern is with my sodium levels. The measurement was 149.6 mg/L. Everything else seems fairly normal, maybe other then chloride levels which are 49.1 mg/L. Should I be worried? Would a reverse osmosis set up even help this? I am guessing...

I got a 1m x 1m space in a small tent where i want to experiment with ebb and flow. However buying a table isnt really a option as everything i can find on local shops is not deep enough. I've seen people advise using self build sandbox with pond liner as bottom..But i don't understand, how to...