Acceptable PPM of water for Semi hydro?

[stripyorchids]

I am interested in trying semi hydro and wanted to ask what TDS is the upper acceptable level for s/h?
My tap water is 86ppm and I use this to water my orchids in bark medium but am fairly sure that is too high for s/h.

I don't have an RO system, I don't have enough orchids for it to be worth it. I can buy fairly cheap containers of deionised water (0ppm) from my local Tesco just to try it out but that's not a sustainable solution long term. I do want to buy a water filter but I am not sure how effective those are. I did see an article that suggested that filters halve the TDS, if that is the case would ~43ppm be usable or is that still too high? What do you suggest?

Thanks in advance!