How many gallons of fresh water can a cruise ship make in a day. Does the gray water get dumped into the ocean? Are the gray and black water kept separate or run together? Is it safe to drink the water from the bathroom faucet?
I'll start with the question of the water being safe to drink. Yes, yes it is. I drink it all the time and I see all that happens.
When the water is produced it is pure water, it has no impurities or even the minerals we naturally consume when we drink water.
All the water produced onboard (methods will be discussed below) is put through a process. The water passes through a tank called a mineraliser, this tank contains calcite. As the water flows through it picks up the minerals and becomes mineralised. It also adjusts the pH of the water.
Next the water passes through chlorination before heading to the potable water tank where itll sit ready to be used.
The bridge dictates which tank is getting filled and which one is supplying the fresh water system as it affects stability. The water is then pumped around the ship in a loop so that theres no chance of stagnant water. The chlorine is monitored and kept within a set range to prevent any nasties in the water.
Using my ship as an example which is a similar size to the Dream class; we have two methods of water production, reverse osmosis and evaporator.
The reverse osmosis method uses really really fine filters that only water molecules can pass through.
The evaporator method uses a vacuum to effectively boil seawater at lower temperatures. This saves energy. The evaporator plant generally runs off the waste heat from the main engines, bit this can be supplemented by the boilers if not enough heat is being produced.
Each evaporator can produce 7-800 tonnes of water per day while the reverse osmosis plants can produce around 450 tonnes per day. Roughly 510,000 imp gallons a day.
The majority of the time itll only be the 2 reverse osmosis plants running as cruise ships generally like to plod along so not enough heat is getting generated by the engines. They normally rely on filling up their fresh water at their home port.
The grey water is generally stored in tanks in the engineering spaces and gradually introduced into the sewage treatment system. So when grey water tank fills up its then pumped. So yes, the grey and black water are mixed.
The black water system is amazing yet gruesome at the same time. You have vacuum units situated in the engineering spaces which suck all the stuff humans produce into it. They even have a little window so you can see!
Once these units reach a set level the black water is transferred and processed ready for the bio reactor.
The bacteria that feast on your number 2's do not like fats very much. So we first filter it all through a screen press to remove the solids like toilet paper (once found someomes shirt clogging it up?!).
The stuff thays filtered out has its moisture removed so it's just transferred to an incinerator.
Once your waste has been through two stages of bacteria feasting it is then pumped into a bank of fine filters. These filters are close to the reverse osmosis filters mentioned above. This leaves what we call permeate, this water is then treated with chlorine and either pumped to a holding tank or disposed of overboard. It's worth noting that this water can technically be recycled so it's not harmful to the environment.
Hope that's satisfied your curiosity a little bit.