Water Mains not Overhead
There are a couple of reasons why water mains and sewer lines are not installed overhead. Wire is very light. Pipes full of water or something else are quite heavy.
Plus, the energy cost of pumping the water or sludge up to an overhead location is considerable. The pressure of the water or sludge going down can also rupture pipes.
The electricity on the other hand is not affected by gravity or height.
There are other reasons why underground is not chosen. Utilities classify power in several divisions, based on voltage. These are Transmission, sub-transmission, Distribution, and User. User voltages are typically 120-240 or 120-208 Volts in the US, and a higher 220/440 or 220/400 Volt for Europe. The second set of numbers is for three phase systems.
User systems are most commonly buried. There are places in the US where they are not buried. Yes, it is easier and therefore cheaper to run them overhead, but, since 1964, most communities have attempted to get the lines buried.
The User lines are fed by Distribution systems, typically operating at less than 15 KV. Often, these lines are actually at 7200 -12470 V or 7500-13200 V. These lines are often also buried. But, less often than the User lines.
The Distribution lines are fed from substations that are in turn fed by Sub Transmission lines In older areas, the Sub Transmission lines are 35 KV, in newer areas, they are 69 KV. Voltages greater than 35 KV are almost never buried. The insuation is just not up to the job.
Finally, from the generation stations to the areas where the power is used, there are Transmission Lines. These Transmission Lines are operated at higher voltages. Most are around 500 KV, with some as high as 750 KV or even 1 Million Volts, and some as low as 120 KV.
Generally, the higher the voltage, the smaller the wire that can be used to send a given amount of power. There is also a higher power loss to buried cables that are run underground than those run overhead.
Utilities run Transmission overhead because the lines lose about 25% less power than underground lines do.
Most will also run the sub transmission lines overhead also. This cannot always be done, so there are some of the lower voltage sub transmission lines that are run underground.
The distribution lines and the final drops to the end user are run underground because of regulations. The runs are much shorter, and the amount of power much lower, so the losses there are not as severe as the higher voltage lines.
Superconductive DC power lines would allow for underground transmission lines, but, that technology is still too expensive.
There are some high voltage underground lines, usually cables underwater, but those are special cases, and only run short distances.
Problems that affect underground lines can include lightning strikes, corrosion, excavation errors, water seepage into the cables, and overheating which causes insulation breakdown, and can off-gas corrosive gases at the end termination points.
Deciding when and where to bury cabling is a complex decision that is more often driven by permitting than by anything else.
But, no matter what, if your lines wind up being buried, you will pay for it. The Utilities don't have a magic cash tree. They only get the money from the customers month by month. Your bill pays for everything the Utility does.
Just something to think about. In this context, saying 'they will pay for it', You are They.
