Pure water (distilled, snow), with no minerals or salts dissolved in it, is a poor conductor of electricity. When certain minerals, such as salt, are added to pure water, the water becomes conductive as a result of dissolution that breaks the salt into its components, electrically-positive sodium and negative chlorine. Ocean water is full of dissolved salts and minerals, and represents a superb conductive medium for grounding.
Lakes and rivers contain less minerals and salts than the ocean in general but they are still good conductors. Whether you are standing on the lake or river bottom, or floating or swimming on the surface, you will be no doubt grounded.
Mineral hot springs are famous for their healing and relaxing effects. This is believed to be due to the mineral content of the water. However, since the water is conductive, you are grounding when you soak in hot springs.
In your home, bathtubs and showers involve tap water that contains minerals and salts and so is conductive. If you take a bath and there is a metal part in contact with the water and that metal part is also in contact with some metal pipe going down into the ground, you are grounded! The same is true with showers. If the water you use to shower comes from metal pipes in contact with the earth, the water you shower with is grounded and will ground you.