Greywater systems have reduced water consumption by 40 percent, as population growth, climate change, urbanization, and levels of water have increased, our water supplies have been under a great amount of pressure. Over time, water scarcity has become an escalating global concern, specifically because traditional techniques of using water have become no longer feasible due to severe droughts. Greywater systems have been very efficient in offering an effective solution by minimizing dependence on freshwater supplies. Grey water systems target reusing contaminated wastewater from sinks, showers, and laundries for non drinking purposes that include toilet flushing and irrigation. Normally, water from sinks and laundries are not treated and become a part of greywater, which becomes an issue in the future during prolonged droughts. Being able to treat wastewater and filter the bacteria out of the water, reduces the amount of freshwater being used to water plants that could be stored and used in urgent scenarios including climate conditions. However, even though greywater systems have many positive aspects, the process also contains many substantial challenges due to its variable composition. Greywater contains a variety of “organic and inorganic substances, heavy metals, endocrine- disrupting chemicals ( EDCs), and microbial contaminants)” making greywater a complex source (Budeli & Sibali, 2025).
Figure 1: Taken from NelSol Water, this image shows the process of greywater systems and how each stage impacts particles of greywater differently.
There are four steps to a greywater filtration system, each stage targeting different particles within the greywater. In the Coarse mesh filter, the mesh bag contains gaps where water can be easily filtered, removing hair, lint, and food waste behind. This step is important for preventing filters from being clogged by large pieces of waste. After the water moves through the Coarse filter it reaches the fine filter where the openings for water to pass are much smaller. The filter catches smaller sized particles like pieces of soap, dirt, and debris. The partially filtered water is then refiltered through a sand filter system, which contains a thick layer of sand on top of a thin layer of gravel. The gravel on the bottom of the filter supports drainage and the sand grains contain small particles packed closely together allowing tiny particles to get stuck in between the sand. When water moves slowly through the sand it leads to a biological activity where sand grains trap microorganisms in the filtered water. This forms a biofilm layer made up of good bacteria that removes harmful substances and eats organic waste. A lower infiltration rate leads to more successful bacteria cleaning. After the sand/ gravel filter, the filtered water is passed through a storage tank where water is transported through irrigation pipes to provide nutrients for plant growth.
In terms of greywater, water quality is divided into two categories such as light and dark greywater. Light greywater is described as hand washing and showering. When light greywater is released into bodies of water like rivers, lakes and estuaries, the nutrients in the light greywater become pullatants, however; to plants they are valuable fertilizer. Light grey water considerably has a low organic matter content along with low levels of nitrogen and phosphorus because of soaps and shampoos. On the other hand, dark greywater contains a high level concentration of organic matter including higher levels of phosphorus and nitrogen. Nitrogen levels are depicted by the amount of food waste produced by kitchen sinks and dishwashers, as phosphorus levels derive from detergents. A variety of “ detergents, surfactants, fats and oils, dairy products, and food residues” present challenges in wastewater management (Hamidi, 2025). Difference in pollutants between light greywater and dark greywater requires different processes to avoid health risks.
Grease and oil are two main substances that become a part of greywater once people put grease down their drains. When grease and water mix, a layer called hydrophobic repellent layer forms on the surface of the water. This layer prevents soil from absorbing water leading to clogging its pores and suffocated roots. In addition, soil nutrient uptake is reduced and restricts sunlight and oxygen from reaching plant roots. Without sunlight and oxygen plants cannot perform photosynthesis resulting in root death.
Recycling Greywater positively impacts the global issue of water scarcity, as the growing population will be around “ 420 million by mid 205”, the demand for water supplies will increase, especially in populated cities like Los Angeles with a population of 3 million people (Rain Harvest, 2014). Due to population growth, the cost for water bills have increased as California uses 15 percent of energy for wastewater. In addition, Americans use about “ 160 gallons of water each day” and 25 percent is greywater (2014). For this reason greywater systems are essential for our environment as “50 percent of all water is used for irrigation” highlighting that greywater systems offer an effective solution for saving freshwater and minimizing the use of it (2014). However, although there are several positive aspects about greywater systems there are also a variety of negative aspects. Greywater contains micro-organisms and without proper treatment micro-organisms can pass dangerous diseases, a very serious health risk. Soap, pathogens, and toxic chemicals can create bacterial contaminants in gardens, killing many plants and organisms. For this reason, it’s important to use certain soaps and detergents to reduce high levels of salt and toxic solutions or else the reuse of greywater can hurt our environment. Economically, according to greywater action, greywater systems can range from 100 dollars for self install to about $800 to $20,000 for full installation. The high cost of greywaters is a major impact on society because installing new plumping with dual filtration is an additional purchase. In conclusion, through a utilitarianism lens, greywater systems have a positive social impact on the environment, benefiting everyone equally by saving water that can be beneficial during prolonged droughts.
Figure 2: En-ROADS Impact Graph on the Likelihood of Prolonged Drought. Afforestation (supported by greywater systems) does not impact the likelihood of drought; however, changes to a more closed-loop water management system will help society better use water and thus feel the impacts of droughts less severely.
Greywater systems are not used at the Lawrenceville school, however we use technologies that target saving water. Around our newest building, Tsai, there are permeable pavers which have a specific structure including gaps in between each paver allowing water to pass through and return to groundwater instead of becoming a part of runoff water. In between the gaps that separate each paver there are crushed stones that facilitate water infiltration by acting as a filter. This allows stormwater runoff to be reduced, minimizing flooding and filtering pollutants out of the water returning to groundwater.
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