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Normally a household is connected with 3 different connections:
Water conducts electricity (and can also transport light), why aren't we transporting electricity using plastic water pipes instead of using copper cables?
If you somehow could use water for optical internet, that'd be a 3-in-1 solution.
Water, especially pure water, is a rather poor conductor of electricity. 5–50 mS/m for tap water vs. more like 6E+7 S/m for copper. That's about 10 orders of magnitude, so for the same losses as a 4 mm diameter AWG 6 wire your pipe would have to be 16,000 km in diameter, which would make plumbing somewhat inconvenient. You'd need a return conductor too.
That said, there are times when water (including groundwater) can be used to conduct electricity for transmission, at a cost in efficiency.
It is not clear if you want to use the 'same' water pipes for drinking/showering and electricity.
Assumption 1: Same pipe with water for both water and electricity
Because if you would touch water that has too much voltage/current, you die.
Actually, what happens is:
Even if the water would have the voltage of a battery, you don't want to brush your teeth with water having a voltage different from ground.
Assumption 2: Different pipes with water for water and electricity
Water has much more electrical resistance than copper, which means it would cause a lot of voltage reduction after long pipes filled with water.
I think this is the main reason, other reasons can be (thinking out loud):
Assumption 3: Only inter-house/building pipes
(meaning only using water to distribute electricity within a single building/house).
Water is a poor conductor. Its conductivity may suffice to electrocute yourself in your bathtub, but it's much, much worse than that of copper:
This means that copper is conducting electricity one to ten billion times better than water. A water pipe is thicker than the wires of an electric cable, but this can't compensate such a huge difference.
Note that this answer is only about the conductivity. Safety and other aspects haven't even been mentioned.
Let us assume that the water is hard (ie with a modest amount of calcium in)... the resistance of the water will be modest, but maybe for short distances it'll "be ok".
Once the water gets to your house, you want to remove any potential difference to ground before anyone can touch the water - which would mean that you would have to have a section that is connected to ground and the water.
If you do this, the amount of power you can extract from the electricity is limited because you have been required to short your mains to keep it safe... and a load placed across a short isn't going to be able to draw much.
Further to this, now that you've had to short the mains, there will be a current continually running - meaning a huge amount of power will be wasted.
It gets worse.
Passing a current through water will result in electrolysis resulting in a build up of hydrogen and oxygen in the pipe. Highly reactive gasses in a confined area is what results in explosions.
Simple circuit Answer:
It will never work , even if salt water (lossy), or pure dielectric Dk=80 water ( too small capacitance for a long gap between electrodes.
simulate this circuit – Schematic created using CircuitLab
Your concept results in a short circuit to the grid with no power transfer.
Two big theoretical problems: High VAR load and water flow restriction
although water has Dk=80 the electrodes in C/2 must be large Area/gap to create a large capacitance.
Since the electrode gap in the transmission line end-end is huge , you now have a a very high series impedance and the AC voltage is then attenuated by the impedance Ratio of high series and low load impedance. - thus the small gap would restrict flow of water. - and the shunt capacitance across the grid now acts as a reactive load which although is opposite 90 deg phase to inductive loads would refult in very poor Power Factor and high VAR losses
Other answers have already covered why this isn't a good idea.
What is a good idea is sharing a large-diameter pipe with other services where possible. There are already projects where sewer pipes have been used for fibre-optic connections, instead of digging a dedicated hole in the ground for your fibre. The fibre is small enough that it won't affect the sewer, there's no disturbance above ground along the route of the cable (which as well as being more convenient also makes it much cheaper), and it's better protected from being dug up accidentally. For example, this project around London.
The thicker pipes for drinking water and thicker armoured cables for electrical power are less obvious wins, but could still use this. However most towns and cities already have this infrastructure in place, so there's no reason to change it; and new developments of course are free to lay services wherever they want whilst the diggers are still working. The difference for fibre of course is that it's a new service being retrofitted into the existing infrastructure.
