12 Misconceptions About Water Treatment, Corrected

Mains water is produced to the criteria defined in the relevant regulations and is monitored regularly by the competent authorities. So there is a defined quality framework on the source side.

The differences met with in practice generally arise not at the source but along the way the water travels before it reaches the user: the age of the building’s plumbing, the condition of the tank if there is one and how long the water stands. So the right question is not “is mains water good or bad” but “what is in the water running from my own tap”.

The assessment can only be made by analysing a sample taken at the point of use. We took the subject up in detail in our drinking water quality guide .

That measurement shows the total amount of dissolved solids in the water; it does not state which substances are present. So it gives a total, not a list of contents.

It is therefore not a measure of quality on its own. A high reading can equally show a source rich in minerals; and a low reading gives no assurance against every risk. The measurement is a valuable tool for following system performance; but it does not define whether the water is suitable.

A full assessment is made with an accredited laboratory analysis. We took up what the measurement says and what it does not show in our TDS article .

It is true that while the membrane separates dissolved substances it separates most of the minerals too. That is not a fault but a result of the working principle of the technology; the same mechanism that holds back the unwanted components holds back the minerals.

Against that, the greater part of daily mineral intake comes from food; what water contributes is one part of that picture. So the subject is taken up not as a deficiency but as a choice about taste and balance.

Those who care about the drinking character can choose a cartridge containing minerals at the final stage. That is not compulsory; we took the subject up in a balanced way in our mineral filter article .

A reverse osmosis membrane separates the water into two streams: the treated water that passes through and the concentrate carrying the dissolved substances that cannot. The water going to the drain is that concentrate, and it keeps the membrane surface clean. Without that stream the surface would block in a short time.

So waste water is not a sign of a fault but part of the working principle. There is one distinction, though: on systems with storage, the flow is expected to stop once the tank is full. If the flow never stops, that can point to a different situation and calls for a check.

We took up the factors affecting the ratio and the ways of improving it in our waste water ratio article .

Filter stages do not break; they reach saturation. A saturated stage keeps letting water through but stops doing its holding job. So the observation “the water is flowing” does not show that the stage is still doing its work.

Waiting has a second effect too: blocked stages raise the resistance to flow and lower the pressure reaching the membrane. That both slows production and prepares the ground for the module tiring early.

The interval for changing is not fixed; the quality of the inlet water and the amount consumed are what decide. We took up how to read the signs in our filter change guide .

Descaling products can reduce build-up that has formed and give relief in the short term. But they do not change the hardness of the water; as long as the feed water stays the same, the build-up forms again.

The two approaches serve different jobs: cleaning is a maintenance operation, removing hardness is a preventive measure. They are not alternatives to one another but answers at different stages. Aggressive applications repeated often can also tire the internal surfaces of the equipment over time.

We took up the effect of limescale on equipment and why the lasting answer lies at the source in our hard water article .

Those products do not take the calcium and magnesium out of the water. So the hardness value in an analysis report stays the same before and after the application. That is a measurable and verifiable fact.

On the effects of such products on build-up behaviour, independent scientific assessments set out differing results and the debate continues. So we give no definite verdict here; what can be said is that the hardness value does not change.

The method that actually lowers hardness is ion exchange. We took up how that approach works and how it is chosen in our softening selection guide .

Boiling is a practice aimed at reducing microbiological risks. Against that, it does not remove the hardness of the water, its dissolved salts, its metal content or its chemical components.

And because of evaporation, the concentration of dissolved solids in the water left behind can rise a little. So boiling does not take the place of full treatment; it serves a different purpose.

We set out in a table which problem is solved by which stage at the point of use in our drinking water quality guide article. For the general framework of domestic treatment methods, the US Environmental Protection Agency filtration fact sheet can be consulted.

Clarity gives an idea only about suspended solids. The components in solution in the water cannot be seen; hardness, dissolved salts and metal content cannot be judged visually.

The same holds for smell. Some components are odourless and give no taste; so a sensory assessment produces no full result.

So the decision is rested on a measurement rather than a visual impression. We took up how to take a sample and how to read a report in our water analysis guide .

The colour and sediment that appear in such demonstrations come largely from the material of the electrodes used. So the result observed has more to do with the process itself than with what is in the water.

Every water containing dissolved solids also gives that reaction; a source rich in minerals can produce a similar picture. So a demonstration is not accepted as a method of analysis.

The real measurement of water quality is made with an accredited laboratory analysis. We took up what to look at when assessing a supplier in our firm assessment article .

Softening removes the hardness ions in water by ion exchange and prevents limescale build-up. Its aim is to protect the plumbing and the equipment; drinking water quality is not the purpose of that stage.

In softened water the dissolved solids load is largely preserved; only the hardness-forming components have changed. So building a separate treatment line in the kitchen is a common approach.

The right build generally has two layers: softening protects the plumbing, while the stage in the kitchen treats the drinking and cooking water. The two systems do not take each other’s place.

Price can give an idea about component quality but is not a sufficient indicator on its own. Three headings are what decide: how well the unit suits your water, the quality of the components inside it, and the service and continuity of spare parts behind it.

Money paid for a problem your water does not have produces nothing in return. In the same way a system whose spare parts cannot be found becomes unusable in a short time, however much it cost.

We took up the assessment criteria in our unit assessment framework, and the items that make up the price in our price guide .