Yeah it is, i'll try another measurement later and see if it changes. But this company is rubbish. From a BP petrol station. You did say these places are no good these days 
What is the highest TDS you would consider acceptable and safe to use in a battery ?
Is a TDS measurement sufficient along with visual inspection for no suspended matter.
Goal here seems to be 0 TDS, what if it was say less than 5.
Aquafina goes through a 5 stage filtration process, i'd imagine they have quality standards that could be verified with a TDS meter if that is all that is necessary to gauge water suitability for lead acid batteries.
I think the TDS meter is ok. Water out the tap comes in at 140ppm, from the aquaguard similar.
This distilled water at 23, aquafina at 3. So there is a range of values there for reference.
