Water is a precious resource and with attendant water scarcity as predicted by many climate change simulation models, there is strong impetus in many countries for increasing the source of fresh water as well as improving water conservation efforts.
One popular conservation efforts is in the reuse of low contaminant water for washing applications. One example could be the reuse of water used in washing rice prior to cooking for watering your plants. But, on a larger scale, there are also efforts in many industries in Singapore to reuse rainwater for various washing applications. Specifically, there is an initiative by the mass rapid transit system in Singapore to collect rainwater at their maintenance base for use as water to clean train cars.
While potentially saving significant quantities of water previously required for washing train cars, reuse of rainwater may pose more problems than it solves, and incur more expenses and costs in the end. Specifically, rainwater tend to be slightly acidic due to the dissolution of sulfur dioxide and nitrogen oxides in the water; thus, prolonged use of rainwater for washing train cars may result in enhanced corrosion of the steel plates lining the train bodywork.
Additionally, there are myriad particles in the air, of different sizes and shapes, that dissolve in rainwater. Hence, rainwater can be characterized by the particle load content it carries, which could have an abrasive effect on the paint work of the train car as typically, high speed jets of water are used to spray clean the train car.
Collectively, while using rainwater for washing train cars help reduce water usage, it carries significant downsides not obvious to the uninitiated. Specifically, dissolution of many pollutant gases such as nitrogen oxides and sulfur oxides in rainwater render the water slightly acidic, which has untoward effects on the steel bodywork of the train car such as enhancing corrosion. In addition, the particulate load of the rainwater is higher than potable water out of the tap, which when channeled through the high speed jets typically used in industrial washing applications, can cause substantial abrasion to the train surface. Altogether, using rainwater for washing train cars, solve one problem but generates many other and increases overall cost and expense.
Tags: rainwater, water conservation, industrial cleaning, abrasion, corrosion, particulate content, acidic,
Acknowledgement: Ng Wenfa thank Seah Kwi Shan for co-authoring this blog post.