Meaning: 'Smart' refers to advanced technology that enhances efficiency, in this case, systems designed to capture rainwater.

Wrong options:

• irrigation: Irrigation refers to the artificial application of water to land, which does not describe the systems intended for rainwater capture.
• impermeable: Impermeable is an adjective that describes a surface that does not allow water to pass through, which does not fit as a descriptor for systems.
• awareness: Awareness is a noun that refers to knowledge or perception of a situation, which does not grammatically fit as an adjective here.
• greywater: Greywater is a noun referring to wastewater from sinks and showers, which does not describe the systems being installed.
• recreational: Recreational is an adjective that pertains to activities done for enjoyment, which does not relate to the context of water conservation systems.
• tool: Tool is a noun that refers to an instrument used to carry out a particular function, which does not fit as a descriptor for systems.

Correct answer: greywater

Explanation: The term 'greywater' is appropriate as it refers to wastewater that can be reused for non-potable purposes, fitting the context of rainwater capture for practical use.

Meaning: Greywater is the wastewater generated from household activities like washing dishes or bathing, which can be reused for irrigation or flushing toilets.

Wrong options:

• irrigation: Irrigation refers to the process of applying water to crops, which does not fit as a purpose for captured rainwater in this context.
• smart: Smart is an adjective and does not fit as a noun for the purposes of water reuse.
• awareness: Awareness is a noun that refers to knowledge or understanding, which does not fit as a purpose for using captured rainwater.
• recreational: Recreational refers to activities done for enjoyment, which does not align with the practical use of captured rainwater.
• tool: Tool is a noun that refers to an instrument, which does not fit as a purpose for the use of rainwater.

Correct answer: impermeable

Explanation: The word 'impermeable' is an adjective that describes a barrier that prevents water from passing through, fitting the context of creating green spaces that reduce runoff.

Meaning: Impermeable refers to a surface that does not allow fluids to pass through, which is relevant in the context of managing water runoff.

Wrong options:

• irrigation: Irrigation refers to the application of water to land, which does not describe a barrier.
• smart: Smart is an adjective that does not describe a physical barrier but rather technology, which does not fit here.
• awareness: Awareness is a noun that does not relate to the physical characteristics of a barrier.
• greywater: Greywater is a noun referring to wastewater, which does not describe a barrier.
• recreational: Recreational refers to activities for enjoyment and does not fit the context of a barrier.
• tool: Tool is a noun that refers to an instrument, which does not describe a barrier.

Correct answer: adopting

Explanation: The term 'adopting' is a verb that fits grammatically and contextually, indicating the action cities are taking to implement smart sensors for monitoring water usage.

Meaning: Adopting means to take up or start to use something, in this case, smart sensors for water management.

Wrong options:

• irrigation: Irrigation is a noun that does not fit as a verb describing the action of cities.
• smart: Smart is an adjective and does not fit as a verb in this context.
• awareness: Awareness is a noun that does not describe an action taken by cities.
• greywater: Greywater is a noun and does not fit as a verb for the actions of cities.
• recreational: Recreational is an adjective that does not describe an action taken by cities.
• tool: Tool is a noun that does not fit as a verb describing the actions of cities.

Correct answer: tool

Explanation: The word 'tool' is a noun that fits grammatically and contextually, referring to an essential instrument or means for achieving urban water conservation.

Meaning: Tool refers to an instrument or means used to carry out a particular function, in this case, promoting water-saving practices.

Wrong options:

• irrigation: Irrigation is a noun that refers to the application of water to land, which does not fit as a means of promoting conservation.
• smart: Smart is an adjective and does not fit as a noun in this context.
• awareness: Awareness is a noun that refers to knowledge, which does not fit as a practical means for conservation efforts.
• greywater: Greywater is a noun referring to wastewater, which does not fit as a tool for conservation.
• recreational: Recreational is an adjective that does not describe a means or tool for conservation efforts.
• adopting: Adopting is a verb and does not fit as a noun in this context.