"drainage" of gasoline-powered vehicle?

A fuel cells vehicle runs by utilizing the energy generated through the reaction between hydrogen and oxygen molecules, and discharges water at the same time (see "drainage" of fuel cell vehicle?)
Addressing the drainage of fuel cell vehicle made me wonder, then, how much of water does a gasoline-powered vehicle dischage?

To calculate the water quantity, we must first know the fuel efficiency of the gasoline-powered vehicle. According to a survey,^[1] the most fuel-efficient car among gasoline-powered vehicles (maybe in Japan?) in the fiscal year 2019/2020 was "SWIFT" by Suzuki Motor Cooperation. Its fuel-efficiency is 18.4 [km L^-1].^[2] By taking its inverse, we learn that SWIFT consumes 54.3 [mL] of gasoline while running for 1 [km].

As the next step, we need to know the quantity of water generated when combusting a unit quantity of gasoline. We must know the chemical formula of gasoline, however, it is a bit tough task to accurately determine it because the gasoline is a mixture of hydrocarbons. Therefore, herein 2,2,4 trimethylpentane (iso-octane) would be taken as a model, which is used as a basis of the Octane rating.^[3]

iso-octane
chemical formula: C₈H₁₈
molar mass: 114.23 [g mol^-1]
density] 0.690 [g mL^-1]

The following equation describes the combustion of iso-octane:
C₈H₁₈ + 12.5 O₂ --> 8CO₂ + 9H₂O ...(1)
Nine times greater quantity of water is generated than that of consumsed iso-octane.

Using the above-obtained numbers, we can determine the total ammont of water discharged by the gasoline-powered vehicle. Iso-octane of 54.3 [mL] corresponds to 37.5 [g] (=54.3 [mL] * 0.69 [g L^-1]), which equals to 0.328 [mol] (= 37.5 [g] / 114.23 [g mol^-1]). On a separate note, the molar mass of water is 18.0 [g mol^-1]. Finally, it is calculated that 53 [g] (=0.328 [mol] * 9 * 18.0 [g mol^-1]) of water is discharged by the gasoline-powered vehicle after a drive for 1 [km].

For your information, this amount of 53 [g km^-1] is similar to 59 [g km^-1] for the fuel cell vehicle determined in a previous post (see "drainage" of fuel cell vehicle?). It is not true that "fuel cell vehicle discharge more water, causing an issue".

Reference

1. 株式会社イード, "『e燃費アワード2019-2020』を発表 実燃費ランキング、総合部門1位はトヨタ『アクア』", https://www.iid.co.jp/news/press/2020/031801.html (accessed on 2020/02/01)
2. e燃費, "e燃費アワード2019-2020", https://e-nenpi.com/award/award20192020/ (accessed on 2020/02/01)
3. 独立行政法人 石油天然ガス・金属鉱物資源機構 石油・天然ガス資源情報, "オクタン価 [おくたんか]", https://oilgas-info.jogmec.go.jp/termlist/1000297/1000376.html (accessed on 2022/02/01)