Before connecting wire antenna's earth bit to water pipe, I checked the connectivity of the wall's 230V mains socket E pin and the copper water pipes under the sink, and there was NO connectivity.
So it was clear to me, the copper water pipes have not connected to any mains earth system, so antenna's earth was connected to the outside tap of the wall in the garden.
The antenna worked quite well apart from 80M. It was giving a lot quieter reception. I heard VY2 KC1 on 40M, and on 80M. There was hardly any hash noise at all. But due to the length of the wire not adjusted for the 80M , SWR lowest tuned was 3:1.
There was absolutely no problem with any sort of interference on anything, when using the antenna. And there was no RF feedback or RF in the shack either. So, it has been working OK for a few days.
But now, I have a 1:1 balun arrived yesterday, so took the antenna down, and configured as Inverted dipole for 40M. It seems working quite well.
I am still not understanding your comment
"at least one Mains scoket E pin is connected to the water pipe," when none of them is connected. I used 2x different DMMs checking all the sockets against the water pipe, and none of them have connectivity at all. I would imagine that the E pins are connected to some sort of public earth system, which has nothing to do with the water pipes. But maybe it is something to be asked and confirmed with the electric company? - I will ask when the meter checking person comes to read the meter next time
But the mains electrical system has been working fine for last 70 years in this house. I am not so sure if it makes sense, that suddenly to ask qualified electricians if the electric supply system in this house is right or not, when there is no problems in electricity supplies, or on any appliances or on anything, just because someone is suggesting to do so.
Anyway, I am now using Inverted V dipole with 1:1 balun cut for 40M, and it seems working even better than the previous antenna. It seems tuning up well on 20M and 15M as well.