These days, any cruise ship is like a huge city, where every detail is thought out so that passengers feel just as comfortable as on land, only better. You can take a shower, do the laundry, or swim in a pool. But where does all the dirty water go? The average ship spends about 40-50 gallons of water per passenger every day. It makes tons of wastewater that needs to be utilized. Say, the world's biggest cruise ship, Harmony of the Seas, can carry about 5,500 passengers together with 2,300 crew members. They produce about 312,000 gallons of wastewater daily! 

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