Issue link: https://maltatoday.uberflip.com/i/1473504
STORMWATER falling on roofs and roads in urban areas can be safely re- used for flushing toilets, laundry, wash- ing floors, industrial use and irrigation and even in recharging the underground water table – without posing any signif- icant health hazards. That is what new guidelines on Green Stormwater Infrastructure (GSI) from the ministry for public works and plan- ning propose in a comprehensive docu- ment that includes contributions of hy- drologist Marco Cremona and architect Philip Grech. The document aims at putting to bet- ter use the 175 million cubic metres of rainwater which falls on Malta, a sub- stantial part of which is lost by falling on impermeable surfaces in urban are- as. This is over five times the total volume of water produced by the Water Servic- es Corporation (WSC) from desalina- tion and groundwater sources. And even one single storm, like that which occurred on 25 November 2021 during which 75mm of rain fell in few hours in the morning, can provide an enormous amount of water: an estimat- ed 23.6 million cubic metres of freshwa- ter in a single morning. "Although it is unrealistic to design systems that can manage all this rain- water within few hours for good use, the percolated rainwater can make a positive difference," the document states, proposing this rediscovery of a "precious resource" through sustaina- ble stormwater infrastructure for new or retrofitted buildings, and infrastruc- tural projects. Urban runoff safer than rural one Sampling in October 2021 and Janu- ary 2022 shows that contrary to public perception, despite high traffic volumes and the occasional overloading of san- itary sewers during extreme storms, urban storm water is not exceptionally contaminated and generally contains low concentrations of heavy metals (in- cluding lead), fluoride and PAHs (Poly- cyclic Aromatic Hydrocarbons). Samples of runoff water from roofs of schools in densely populated, heavy-traffic urban areas also showed very low concentrations of heavy met- als. Urban runoff does not contain high levels of chloride and nitrate which are the major contaminants of groundwater in Malta. The results, though not exhaustive, indicate that urban stormwater is not exceptionally contaminated, facilitating the construction of infiltration systems such as soakaways, pervious pavements, filter-strips and other means of indirect groundwater recharge in urban areas. On the other hand, studies on the quality of runoff along valleys present a rather negative picture, due to severe contamination from animal waste nu- trients, particularly nitrates. The study does not recommend groundwater re- charge systems using rural runoff water. How to recover rainwater Various technologies can be designed to divert, capture, and store rainwater, the most common being traditional 14 maltatoday | SUNDAY • 17 JULY 2022 NEWS Rediscovering rainwater as a precious resource Government report with concrete proposals on how to reuse rainwater recognises risk resulting from over- development which has increased impermeable surfaces that prevent rainwater from reaching the aquifer JAMES DEBONO Sampling in October 2021 and January 2022 shows that contrary to public perception, despite high traffic volumes and the occasional overloading of sanitary sewers during extreme storms, urban storm water is not exceptionally contaminated and generally contains low concentrations of heavy metals