The ocean – definitely! As the salt in the water is conductive – thus the earth’s free electrons travel through the water to you 🙂
Fresh water lakes and rivers – yep! Even though they contain less minerals and salts – for conductivity the free electrons still travel through the water. Walking along the bottom is the best though.
Mineral Hot springs – these are already well known for their healing properties, but it is more than the mineral content. The excess minerals makes it a great conductor for the earth’s free electrons.
Swimming pool – the jury is still out on this one. If you were in the water and hanging your arms over the side and touching the ground – then of course. But otherwise not really.
Showers, baths etc. in the house? – Tap water contains minerals and salts, but depending on how chlorinated the water is could be an issue. If the tap that the water is coming out of is metal and that metal is connected to a metal pipe that goes into the ground then yes. Just remember though that the fixture that the water comes out of may be metal, but the pipes into the ground may be polypipe not metal. So unless you are confident that the plumbing is all metal – I wouldn’t guarantee that you are being grounded.