Conductivity in water?

[Barry Tetra]

Hi everyone.

I am going to enter BADC 2022 and I need scientific explanation for this following questions:
1. What is conductivity? Is it the same as TDS?
2. Does low conductivity related to low pH?
3. Is poor mineral content the same as low conductivity?



Cheers Barry

 

[Oblio]

Hi everyone.

I am going to enter BADC 2022 and I need scientific explanation for this following questions:
1. What is conductivity? Is it the same as TDS?
2. Does low conductivity related to low pH?
3. Is poor mineral content the same as low conductivity?



Cheers Barry

Conductivity is a measure of how easily free electrons flow in the presence of an electric field. The reciprocal (or inverse) is resistivity. It is not the same as TDS, though TDS creating ions will increase the conductivity. As an example, pure water has a very low conductivity (near zero), add some salt and the conductivity rises by several magnitudes.

Here is a great video. I warn you, you may become addicted and spend hours watching the lectures.

 

[StevenF]

1. What is conductivity? Is it the same as TDS?
2. Does low conductivity related to low pH?
3. Is poor mineral content the same as low conductivity?

conductivity is how easy it is for electricity to flow. Pure water doesn't conduct electricity. But if you add minerals (it doesn't take much) to it it does conduct . TDS stands for Total dissolved minerals are solids. So TDS and conductivity are related but different. The most accurate way to measure TDS is take a sample of water, Evaporate the water and measure the weight of what is left. But that takes time. So TDS meters pass electricity through the water and translate it to TDS. But since the conductivity minerals depends on the elemental composition two different samples of water can have the same conductivity but drastically but different mineral content. So the accuracy for TDS meters is dependent on the minerals in the water.

PH is the ratio of acids to bases in the water. Acid and bases may be minerals or just gases but both will affect conductivity. However you cannot translate conductivity to PH. You could have three sample of water one acidic and one neutral and one basic but all could also have the same conductivity. A PH reading of 7 is neutral. PH of less than 7mis acidic and a PH of more than 7 is basic.

 

[Oblio]

pH is (simplistically speaking) the logarithmic concentration of Hydrogen ions. Since it is logarithmic, a pH of 8 has 10 times the amount as a pH of 7.

 

[TwoTankAmin]

1. What is conductivity? Is it the same as TDS?
"Electrical conductivity tells us how well a material will allow electricity to travel through it."
A conductivity meter has a pair of electrodes with a space between them. They are submerged in the water and a small current is sent out of one electrode. How much reaches the other other electrode determines the conductivity of the water. As noted pure water is a poor conductor.

Conductivity is usually measured in micro- or millisiemens per centimeter (uS/cm or mS/cm).

"TDS stands for total dissolved solids, and represents the total concentration of dissolved substances in water. TDS is made up of inorganic salts, as well as a small amount of organic matter. Common inorganic salts that can be found in water include calcium, magnesium, potassium and sodium, which are all cations, and carbonates, nitrates, bicarbonates, chlorides and sulfates, which are all anions. Cations are positively charged ions and anions are negatively charged ions."

Note that nitrite and nitrate etc. are ions and they contribute to conductivity/TDS.

TDS are similar to conductivity, A TDS meter is basically a conductivity meter which uses a formula to convert the micro-siemens into ppms.

I have a continuous monitor on a tank. It gives the choice between using a reading of Conductivity or either of two different formulas for TDS. I can make sense of ppm easier then micro-siemens so I set it for TDS.

Bear in mind the conductivity/TDS tells us nothing about what exactly the water contains. It only gives one a good Idea of how much stuiff in total is there.

2. Does low conductivity related to low pH?
Usually this is the case. But then lower pH also relates to soft water. Soft water means there is less stuff in it. However, this is not a 1 to 1 relationshsip. You can have different levels of conductivity at any given pH reading. But the general rule is they are both similar- low pH and lower conductivity and higher pH and higher conductivity usually go together.


3. Is poor mineral content the same as low conductivity?
Basically, yes. Simply put. "A mineral is a naturally occurring inorganic solid, with a definite chemical composition, and an ordered atomic arrangement." So that is a lot of what is dissolved in water.