I think that small goods , like water, should take up less space than large goods. It seems odd for a ship bay of 22 units to be able to hold 22 big things and then only hold 22 smaller things. Often margins are good on low price, high volume trading. But the system doesn't encourage that avenue in a fair way. It actually de-incentivises it. Ships holds should be filled on a Volume or Mass basis rather than a unit per item basis. This would make the economic trading aspect more enjoyable and give it a more realistic feel.

Now that is an interesting suggestion.

Can you elaborate more upon this topic?

How do you know the volume of one cargo unit of water, genius?

We already have this dude. Not all objects use 1 cu of space. Consumer Robotics, for example, use 3 cu. EC class ships, if you happen to find one in item form, use a good 100 cu.