Water, simple and necessary, threatens vulnerable citizens throughout the world. The need for safe drinking water is severe. There are two obstacles to providing clean water: the “inadequacy” of local supplies, and the presence of contaminants. How can better design find solutions to this growing problem?
There are often seasonal differentials in water supplies, when excess precedes drought. The ability to find and store water was essential to human development, with the discovery of how to find and protect water sources, and how to keep water in every size of vessel from a clay pot to a reservoir. Human life requires a minimum of 1 liter of drinking water per person, per day. We use much more: the average citizen in the U.S. uses 575 liters/day, a citizen of India uses 135 liters.
Public water distribution systems allow many the luxury of forgetting the drudgery of collecting, transporting, and storing water. In places without reliable infrastructure, collecting water requires significant time and energy that could be spent by children studying at school, or by women at work.
Extending infrastructure to serve all people comes at a high cost. In urban areas with high densities, this cost is borne by the great number of people. Rome constructed nine aqueducts by the year 52 to provide water for a population of nearly one million. Roman engineering not only provided the distribution system but built storage to guard against evaporation, interruption, and defilement. The basilica cistern in Istanbul is a wonder of architecture with carved capitals and vaulted ceilings, constructed to house only water.
Massive engineering projects of the last 100 years include hydroelectric dams and channelized water, resulting in long-term environmental degradation. These community-scale “solutions” harmed natural cycles, but direct new efforts to site-scale, self-sufficient alternatives that capitalize on existing technologies and products.
Streets and buildings may become the new aquifers to collect and store water. In urban areas, green spaces may be “manufactured” by reclaiming and transforming brownfields and impervious edges along streets. Green boulevards enhance the aesthetic quality, and also collect, filter and store stormwater in swales, restoring water to the aquifer through groundwater recharge and to the atmosphere through vegetation. Options to impervious surfaces for roads and parking are growing with pervious concrete, interlocking pavers, grasspave or gravelpave systems. In addition, green boulevards cool the microclimate and reduce the heat island effect.
Construction of waterworks is incomplete without purification. A number of techniques are available to remove contaminants using physical processes (filtration), biological processes (microbes), chemical processes (chlorination), and electromagnetic radiation (exposure to UV light). These techniques are resource-intensive and require community-scale facilities to remove solids, salts, organic pathogens, and toxic ions.
One promising technique is solar disinfection using plastic bottles exposed to direct sunlight. UV wavelengths react with oxygen dissolved in the water to produce hydrogen peroxide that damages pathogens and destroys cellular structures of bacteria. The use of titanium dioxide film over glass cylinders in conjunction with solar disinfection took only 15 minutes on a sunny day to render coliform bacteria undetectable in trials, and the water remained free of bacteria for seven days.
When UV radiation is not available due to rainy weather, rainwater harvesting may be employed. Most buildings have some form of rainwater collection: gutters, roof drains, scuppers, and downspouts. These building elements are an asset for collecting rainwater; all that remains is the storage component. Project-scale collection systems collect, channel, treat, and store rainwater on site until needed by the building users. South-facing metal roofs overlaid with TiO2 glass tubing can collect, purify, and store rainwater for potable water. This system has the added benefit of providing hot water, lowering energy use.
And finally, not all water has to be treated to drinking water standards. Rainwater and greywater captured from showers and sinks may be used for flushing and irrigation. Buildings may repurpose “used” water for non-potable functions; this slightly used resource offers a measurable contribution to the global water cycle, the endless connection between vapour and beverage, droplet and sea.