I should add that the tonne is a measure of mass so, technically, items have a 'mass of 10 metric tons', not 'weigh 10 metric tons'.

In SI, the 'tonne' (1000 kg) is spoken as 'metric ton'. So, the written sentence, 'I bought 1 tonne of coal', should be spoken as, 'I bought one metric-ton of coal'.

Expressions, such as 'He has tons of experience' (which was in use long before metrication) would, clearly, sound ridiculous of spoken as 'He has metric tons of experience'.

'Water' does not, by definition, mean water in its liquid state; it also applies to its solid state (ice) and its gaseous state (steam). There is absolutely nothing wrong with the term, 'liquid water', The term is used when it's necessary to distinguish water in its liquid state from its solid or gaseous states. In the case of Mars, we know that there are large areas of ice but to discover water in its liquid state is something else.