Modelling of a roof runoff harvesting system: The use of rainwater for toilet flushing

The water balance of a four-people family rainwater harvesting system was calculated in a case study. The experimental water saving efficiency (WSE) was calculated as 87 %. A simple computer model was implemented to simulate the behaviour of the rainwater harvesting system. In general, the rainwater collector volumes predicted by the daily model had shown a good correlation with the experimental values. The difference between the experimental and the predicted values for the stored volume can be explained by the lack of maintenance of the system that can affect its performance. On the basis of a long-term simulation of 20-year rainfall data, the following parameters were calculated: rainfall, water demand, mains water, rainwater used, over-flow and WSE. The collection of rainwater from roofs, its storage and subsequent use for toilet flushing can save 42 m3 of potable water per year for the studied system. The model was also used to find the optimal size of the tank for the single-family household: a storage capacity of approximately 5 m3 was found to be appropriate. The storage capacity and tank size were distinguished. The importance to take into account the dead volume of the tank for the sizing was indeed highlighted

Water quality monitoring and hydraulic evaluation of a household roof runoff harvesting system in France

The quality of harvested rainwater used for toilet flushing in a private house in the south-west of France was assessed over a one-year period. Twenty-one physicochemical parameters were screened using standard analytical techniques. The microbiological quality of stored roof runoff was also investigated and total flora at 22°C and 36°C, total coliforms, Escherichia Coli, enteroccocci, Cryptospridium oocysts, Giardia cysts, Legionella species, Legionella pneumophila, Aeromonas, and Pseudomonas aeruginosa were analysed. Chemical and microbiological parameters fluctuated during the course of the study, with the highest levels of microbiological contamination observed in roof runoffs collected during the summer. Overall, the collected rainwater had a relatively good physicochemical quality but variable, and, did not meet the requirements for drinking water and a microbiological contamination of the water was observed. The water balance of a 4-people standard family rainwater harvesting system was also calculated in this case study. The following parameters were calculated: rainfall, toilets flushing demand, mains water, rainwater used and water saving efficiency. The experimental water saving efficiency was calculated as 87 %. The collection of rainwater from roofs, its storage and subsequent use for toilet flushing can save 42 m3 of potable water per year for the studied system

Monitoring of water quality from roof runoff: Interpretation using multivariate analysis

The quality of harvested rainwater used for toilet flushing in a private house in the south-west of France was assessed over a one-year period. Temperature, pH, conductivity, colour, turbidity, anions, cations, alkalinity, total hardness and total organic carbon were screened using standard analytical techniques. Total flora at 22°C and 36°C, total coliforms, Escherichia coli and enterococci were analysed. Overall, the collected rainwater had good physicochemical quality but did not meet the requirements for drinking water. The stored rainwater is characterised by low conductivity, hardness and alkalinity compared to mains water. Three widely used bacterial indicators - total coliforms, E. coli and enterococci - were detected in the majority of samples, indicating microbiological contamination of the water. To elucidate factors affecting the rainwater composition, principal component analysis and cluster analysis were applied to the complete data set of 50 observations. Chemical and microbiological parameters fluctuated during the course of the study, with the highest levels of microbiological contamination observed in roof runoffs collected during the summer. Escherichia coli and enterococci occurred simultaneously, and their presence was linked to precipitation. Runoff quality is also unpredictable because it is sensitive to the weather. Cluster analysis differentiated three clusters: ionic composition, parameters linked with the microbiological load and indicators of faecal contamination. In future surveys, parameters from these three groups will be simultaneously monitored to more accurately characterise roof collected rainwater

Suivi hydraulique et modélisation d'un système de récupération des eaux de pluie en aval des toitures

National audienc

Récupération des eaux de pluie en aval des toitures pour une réutilisation dans l’habitat collectif et privatif: Etude holistique reposant sur le suivi de deux sites

National audienc