Playing with a cheap water quality TDS meter

[thinwater]

This thread highlights the nature of the consumer water filtration business, which focuses on selling "safety" to non-chemists and non-biologists that don't know what they actually need. They just want "safety" or "better taste", without understanding what that requires or what it means (safe from what?).

 

[Hydrozoan]

... The positively charged ions are attracted to the negative electrode , or cathode, and are therefore called cations. The negatively charged ions ions are attracted to the positive electrode, or anode, and are therefore called anions.

I believe we have Faraday to thank for the nomenclature

Yes, though William Whewell (one of the many C19th polymathic Anglican priests) suggested the terms to Faraday at the latter’s request for help with terminology.

The whole business is confusing because conventionally current was considered as a flow of positive entities, not of electrons, so it flowed down from the anode - Greek ‘up’ (ánō) and ‘way’ (hodos) - to the cathode - Greek ‘down’ (káto). Which is why cation and anion in turn were attributed as they were, using the Greek for 'going' (ion).

I hope that is correct - and that it may (perhaps) help to further clarify the matter.

 

[Yngmar]

We have a TDS (and a less useful pH) meter and use it to check water supplies before filling up the tanks. We also do a taste test.

We use the TDS reading to guesstimate how much sodium hypochlorite to add. I know it's not ideal for that, but it's far better than nothing and avoids overdosing when the water is already very good.

An additional highly scientific test we perform is washing the boat with the water. This actually tells you a lot about what's in the water - after the drops have dried on the glass windscreen. If they leave white scaly stains on the windows, it was mostly calcium - i.e. just hard water. If they leave crystal residue that attracts moisture in the night, it was residual salt, common for desalinated water (not salty enough to taste, but enough to measure and leave residue). Once or twice we also had water with high TDS (800 ppm) that left some kind of sticky stuff after drying. Presumably something biological. We treated with maximum safe dose and had no problems.

Only funny water we got was in Siracusa, where the water had a whopping 1800 TDS (I thought the meter was broken) and tasted salty. The locals (and Google) said the entire town's water is like that, as the regional agriculture has depleted the water table to the point where seawater enters it through the porous volcanic rock. This is mostly a problem near the end of the season, when the snow on Mt. Etna has melted away and stopped replenishing it until winter. It's apparently safe for consumption, and we did a few times, but for taste reasons mostly resorted to drinking from the emergency stash of bottled water stowed in the bilges until then (salty tea is not nice). We were happy to empty it from the tanks as soon as we got to the next place with a tap.

We always drink from the boat tanks without further filtration. No problems, apart from salty Siracusa and if we overdose the treatment it can taste a bit funny, although this soon evaporates, and since we started using the TDS meter, we rarely over-treat anymore.