Pure Water and Electricity Conduction

No. Pure water will conduct no electricity at all.

It's a good insulator.

That's not exactly true. Conductivity is low because water only ionises slightly, but at 25°C it is 5.4 μS/m.

OK.

I knew someone would take issue with total nonconductivity, but was hoping to keep it simple. Most people don't have equipment that can measure microconductivity.

Agreed, perhaps we should add, in case the OP gets the wrong idea, that in most practical situations, eg standing in a puddle working on electrical kit, the conductivity is quite high, but it's nearly all down to dissolved ions, not the water itself.

No...

Pure water is a much better conductor than ultrapure water, Murphy.

Au contraire.

No! Very pure water has low conductivity (high resist ivory).

Define 'pure', please?

No, "pure" water is not very good as compared to sea water or even fresh water with natural minerals and impurities.

Salty water is as good as copper conductor for conducting electrical current. HVDC (High Voltage DC) transmission across sea or islands utilizes this property and power transmission needs only one cable for supply current and return current will be sea water.

In 1986, I was working on electron accelerator that needed 400kV to accelerate the electron. The whole structure of accelerator station was supported on the four (4) columns of insulators whose insulating rating of each column was 400kV AC with respect to ground.

I sat many times on 400kV live station and was monitoring and adjusting some instruments. There were some instruments that were required heavy cooling due to high heat generation in them. To cool these instruments having high heat generation, water was circulating on them and these instruments were on the 400kV live station. Water circulating pump was on the ground which was on ground or zero potential.

Since water was flowing from ground potential (pump location) to 400kV station through pump. To avoid the insulation break down between ground and 400kV station due to connection of water between them.

The water pump was installed with filters that were removing salts from circulating water. This circulating water pipe was installed with a meter which reads the electrical insulation of water. Water electrical insulation was maintained at 18MegaΩ(Mega Ohms) and that was sufficient to insulate between pump on the ground and 400kV station. Because instrument on 400kV station and Pump on ground both of them was connected by circulating water having 18Mega-Ohm insulation.

Therefore purity of water is measured in terms of it insulation level for electrical purpose. 18Mega-Ohm water insulation level is sufficient even for 400kV withstanding capacity.

Therefore water with very, very & very low salts content( nearly pure) is not a electrical conductor but it is an insulator.

I suppose you mean 18 megohm.cm?

The meter shows only the reading in 18Mega-Ohm. It is the level of purity of water from all kind of Salts( amount of mineral content in water). the less the minerals content in water the more increases it's insulation level.

It's just that ultra-pure water has conductivity 5.4 μS/m (see #6) and resistivity = 1/conductivity = 0.18 megohm.m = 18 megohm.cm.