Due to the combined effect of intense rainfall events together with the expected impact of climate change, this will put pressure on the existing and future infrastructure for storm water management. One of the challenges related to this is the combined sewer system which is still operating in large areas of many cities worldwide. In Stockholm, combined sewer represents around 50% of the total sewer pipe length. In a Combined sewer system, once the conveyed discharge exceeds the system capacity, the system overflows, which can result in a diverse range of health and environmental problems. The cause of overflow has been strongly linked to runoff from intense rainfall events. Therefore, a key proposal to overcome this problem is to disconnect runoff from hard surfaces. This research aims to investigate the impact of applying a rainwater harvesting (RWH) and reuse system to collect runoff water from roof surfaces in areas with combined sewer system. A simulation water balance model for a rooftop RWH system was developed and two reuse purposes were considered, which entails toilet flushing and garden irrigation within the property. The study area consists of one building block within Kungsholmen area in Stockholm. The obtained results indicate that applying such systems can reduce runoff to the sewer system. Toilet flushing reuse shows a higher reduction impact on sewer flow than the use for irrigation. Toilet flushing reuse reduces annual runoff volumes to sewer in a range of 49.5% - 93.4% while irrigation provided reduction in a range of 11.6% - 26.3%. Regarding number of times that overflow from the combined sewer system occurs, toilet flushing reuse demonstrated reduction of 40% - 100% while 20% to 60% was reduced by irrigation reuse. For overflow volume, a reduction rate of 11% to 100% was reached through toilet flushing in contrast to 9% to 43% reduction from irrigation reuse. 19% to 37% of toilet flushing water demand was covered by the tank, while arange of 48% to 100% was covered for irrigation demand. All these parameters were found to be sensitive to change in tank size where increasing the size result in higher flow reduction rates. When considering implementing a reuse system, it is important to consider the applicability of RWH and reuse within the specific property. In areas that are under development, either of the two reuses can be considered depending on local conditions. However, in already built up area it is difficult to introduce a system that requires significant adjustment to existing pipe networks, such as reuse systems for toilet flushing. Systems for outdoor irrigation are possible to implement in most situations. When it comes to tank size, the optimal size will depend on the intended reuse, the catchment area and the objective of the system. For example, if the main objective is to reduce potable water consumption, a smaller tank can be used compared to where the main objective is to reduce sewer overflow. Hence, when considering implementing a rainwater reuse systems, each project will need to consider the local conditions as well as the individual objectives when determining the optimal reuse purpose and tank size. A cost-benefit analysis should also be considered when determining the optimal tank size for the intended use.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: This study focuses on the water demand of selected residential properties with access to groundwater in serviced areas of the Cape Peninsula. This winter rainfall region is typified by hot and dry summer months, corresponding to peak garden water demand. Water restrictions in the area are relatively common and primarily target outdoor use. Groundwater serves as an alternative source of water to some consumers in the area, but little is known about the extent of such use and the impact thereof on potable water demand. A major part of the area is underlain by a primary, unconfined aquifer that has been reported to have high exploitation potential. Its unconsolidated sand and shallow water table provides ideal conditions for small scale groundwater abstraction. Several owners of properties situated above the aquifer unit have capitalised on this and utilise groundwater as an alternative to potable water, mostly for garden irrigation purposes. The main objective of this research was to investigate the average extent of the expected reduction in average annual municipal water demand due to private groundwater use at the selected properties in the study area. The methodology involved abstracting data from the City of Cape Town’s registration process for the private use of non-potable water. The data was recorded between 2000 and 2006 and was available only in hard copy format. The registration data was used to identify residential properties with access to private groundwater sources, based on the physical addresses recorded on the registration forms. The rate of groundwater abstraction was not recorded during the registration process, nor was any of the properties spatially referenced. The data set contained information for 4 487 properties, of which 3 764 could ultimately be used in the analysis. Data from a recent hydro-census in Hermanus (which was done by others prior to this study) was used to test the intended research method first. This trial investigation involved only 114 properties and was used to streamline the proposed methodology for application on the full-scale analysis of the City of Cape Town data. Each address was captured electronically, verified manually and filtered to extract only those representing residential properties for which groundwater use was registered. In order to identify the properties spatially, the addresses had to be converted to coordinates through a procedure called geocoding, so as to plot each spatially and obtain the attributes such as stand size, position and the unique Surveyor General’s code. This was necessary in order to link the addresses to the municipal treasury system and obtain their latest available water consumption records using a commercial software package that incorporates consumer information. Next the actual annual water consumption figures were compared with recently published water demand guidelines based on stand size as single explanatory variable. The selected residential stands were divided into pre-defined stand size categories. The average water consumption of all the stands in each size category was calculated and compared with the suggested water demand as per the guidelines used, based on the centre value of the size range of each category. The results of the comparative analysis confirm findings from two earlier studies where lower municipal water use was reported for residential properties with access to groundwater in a summer rainfall region. The results further showed that the mean average annual potable water demand of consumers in the study area with access to groundwater was on average 31.4% lower than those considered without such access in the same region. This represents an average reduction of 333 l/stand/day (about 10 kl/stand/month) in the potable water demand of the selected residential stands. This study therefore confirms that serviced residential stands with access to private groundwater sources in the Cape Peninsula have lower average metered water consumption from the municipal supply system. / AFRIKAANSE OPSOMMING: Hierdie studie fokus op die water anvraag van geselekteerde residensiële erwe met toegang tot grondwater in gedienste woongebiede van die Kaapse Skiereiland. Die gebied is ‘n winterreënvalstreek, met warm, droë somermaande wat saamval met piek water aanvraag vir tuinbou. Waterbeperkings in die area is relatief algemeen, veral op die buitegebruik van water. Grondwater dien as alternatiewe bron vir sommige verbruikers, maar kennis oor die omvang van sulke gebruik, sowel as die impak wat dit het op die aanvraag na drinkbare water is beperk. Die grootste deel van die gebied ter sprake is geleë bo ‘n onbegrensde hoof waterdraer, met berigte hoë ontginningspotensiaal. Die ongekonsolideerde sand en hoë watertafel is ideal vir kleinskaalse grondwateronttrekking. Heelwat van die eienaars van grond wat bo hierdie akwafeer geleë is het die situasie uitgebuit en gebruik grondwater as alternatief vir drinkwater, veral vir tuinbesproeiïng. Die hoofdoel van hierdie navorsing was om die gemiddelde omvang van die verwagte vermindering in gemiddelde jaarlikse munisipale wateraanvraag weens die privaat gebruik van grondwater by die geselekteerde erwe in die studiegebied te ondersoek. Die metodiek het die onttrekking van data uit die Stad Kaapstad se registrasieproses vir die privaat gebruik van nie-drinkbare water behels. Hierdie data, wat tussen 2000 en 2006 vasgelê is, was slegs in harde kopie formaat beskikbaar. Die registrasie data is gebruik om woonerwe te identifiseer met toegang tot privaat grondwater bronne, volgens die fisiese adres verskaf op die registrasie vorms. Die tempo van grondwater onttrekking was nie opgeneem gedurende die registrasie proses nie, so ook nie ruimtelike aanwysings na die ligging van die eiendomme nie. Die datastel het inligting bevat oor 4 487 eiendomme, waarvan 3 764 uiteindelik bruikbaar was in die analise. Data van ‘n onlangse hidro-sensus in Hermanus (wat deur ander gedoen is voor die aanvang van hierdie studie) is gebruik om die beoogde navorsingsmetodiek eers te toets. Die toetsondersoek het slegs 114 eiendomme behels, en is gebruik om die voorgestelde metodologie meer vaartbelyn te maak voor toepassing op die volskaalse analise van die Stad Kaapstad data. Elke adres is elektronies vasgevang, met die hand geverifiëer, en dan gefilter om slegs die residensiele eiendomme waarvoor grondwater gebruik geregistreer is, te behou. Om die ruimtelike verwysing van die eiendomme verder te kon indentifiseer, moes die adresse omskep word in koördinate om sodoende die erwe te kon posisioneer en die erfgrootte, posisie en die unieke Landmeter Generaal kode van elke erf te verkry. Dit was nodig sodat die adresse aan die munisipale stelsel gekoppel kon word om sodoende die jongste beskikbare waterverbruik rekords te verkry deur gebruik te maak van ‘n kommersiële sagteware pakket wat verbruikers-inligting inkorporeer. Hierna is die werklike jaarlikse waterverbruik syfers vergelyk met onlangs gepubliseerde wateraanvraag riglyne, gebaseer op erfgrootte as enkel verklarende veranderlike. Die geselekteerde woonerwe is toe in voorafgekose kategorië verdeel volgens erfgrootte. Die gemiddelde waterverbruik van al die erwe binne elke grootte-kategorie is bereken en vergelyk met die voorgestelde wateraanvraag volgens die riglyne, gebaseer op die middelpuntwaarde van die grootte strekking van elke kategorie. Die resultate van die vergelykende analise staaf die bevindinge van twee vroeër studies wat laer munisipale watervebruik rapporteer vir residensiële eiendomme met toegang tot grondwater in ‘n somerreënvalgebied. Die resultate wys ook dat die gemiddelde jaarlikse drinkbare water aanvraag van verbruikers in die studiegebied wie toegang het tot grondwater, gemiddeld 31.4% laer is as dit van verbruikers wie beskou word sonder sulke toegang in dieselfde streek. Dit verteenwoordig ‘n gemiddelde vermindering van 333 l/erf/dag (rondom 10 kl/erf/maand) in die aanvraag na drinkbare water van die geselekteerde woonerwe. Hierdie studie bevestig dus dat gedienste residensiële erwe met toegang tot privaat grondwater bronne in die Kaapse Skiereiland laer gemiddelde gemeette waterverbruik vanuit die munisipale toevoerstelsel het.

I norra Storstockholm produceras och distribueras dricksvatten av kommunalförbundet Norrvatten. Under värmeböljan sommaren år 2018 ökade dricksvattenförbrukningen bland medlemskommunerna till en sådan hög nivå att Norrvattens tillgängliga kapacitet för dricksvattenproduktion riskerade att inte räcka till. En bidragande orsak till detta, antogs vara att en stor del av den ökade vattenförbrukningen gick till bevattning och fyllande av pooler. Det är ett behov som Norrvattens verksamhet inte är dimensionerad för att hantera. I takt med dagens växande befolkning i Norrvattens medlemskommuner och en hotande global uppvärmning, förväntas risken för kapacitetsbrist tillta. Således var syftet med detta arbete att studera hur behov av vatten för bevattning och fyllande av pooler kan tillgodoses på ett långsiktigt hållbart sätt bland Norrvattens medlemskommuner utifrån de tre hållbarhetsdimensionerna. Med hjälp av litteraturstudier, intervjuer och beräkningsmodeller identifierades alternativa lösningar och effektiviseringsmöjligheter gällande tillgodoseendet av vattenbehov för bevattning och poolfyllning. Dessutom genomfördes en stickprovsundersökning med syftet att studera socioekonomiska faktorer, vid eventuell implementering av de identifierade alternativa lösningarna och effektiviseringsmöjligheterna i Norrvattens medlemskommuner. Därefter applicerades en kvantitativ analys på det erhållna dataunderlaget med väldefinierade statistiska metoder för konfidensintervall och hypotesprövningar på signifikansnivån 5 %. Resultatet visade flertalet alternativa lösningar och effektiviseringsmöjligheter var passande att implementera för att tillgodose behov av vatten för bevattning och fyllande av pooler bland Norrvattens medlemskommuner. Det berodde på en stor välvilja gentemot såväl miljön som Norrvattens verksamhet. Mer konkret identifierades en utbredd vilja att förändra konsumtionsbeteenden gällande vattenanvändning för bevattning och fyllande av pooler. Som en följd fanns också en villighet att betala mindre summor för alternativa lösningar och effektiviseringsmöjligheter för att tillgodose sådana vattenbehov. Dock påvisades även en utbredd motvillighet till kraftiga ökningar i priser och kostnader för knippade med vattentjänster, varpå mer kostsamma alternativa lösningar uteslöts som långsiktigt hållbara utifrån socioekonomiska hållbarhetsperspektiv. Därmed rekommenderades Norrvatten att fortsätta planera för utbyggnation av sin produktionskapacitet, eftersom de identifierade alternativa lösningarna och effektiviseringsmöjligheterna inte ansågs tillräckliga för att nollställa behov av dricksvatten producerat av Norrvatten för bevattning och fyllande av pooler. Samtidigt drogs slutsatsen att behovet av utbyggd kapacitet skulle kunna reduceras vid implementering av de identifierade lösningarna och effektiviseringsmöjligheterna. Dock kunde inte det reducerade behovet beskrivas i kvantitativa termer med den applicerade arbetsmetodiken. Således rekommenderades Norrvatten att i framtiden arbeten genomföra en kartläggning av detta, i syfte att erhålla värdefullt beslutsunderlag kring storlek på utbyggd produktionskapacitet. / In the northern part of Greater Stockholm, drinking water is produced and distributed by the municipal association Norrvatten. During the height of the summer 2018, drinking water consumption among the member municipalities increased to such an extent that the available production capacity was nearly insufficient. This was assumed to be due to major increases in drinking water consumption for garden irrigation and filling of pools, which are water needs that the production capacity is not dimensioned to handle. Furthermore, the risk of production capacity shortage is assumed to increase in the near future due to population growth and global warming. The purpose of this thesis was to examine possible approaches to supply the need for water for garden irrigation and filling of pools among the member municipalities of Norrvatten in a long-term sustainable manner with regard to the three sustainable dimensions. Based on literature studies, interviews and theoretical models, alternative solutions and efficiency opportunities of supplying water needs for garden irrigation and filling of pools was identified. A sample survey was also conducted with the aim of studying socio-economic factors regarding a potential implementation of the identified alternative solutions and efficiency opportunities among the member municipalities. Subsequently, quantitative analysis was applied to the obtained data with well-defined statistical methods for confidence intervals and hypothesis tests at the significancelevel of 5 %. The result illustrated implementable alternative solutions and efficiency opportunities of supplyingwater needs for garden irrigation and filling of pools. It was due to a large benevolence towards the environment and Norrvatten’s operations. More specifically, a widespread willingness to change consumption behaviours regarding water utilization for garden irrigation and filling of pools was identified. As a consequence, there was also a great willingness to pay smaller sums for alternative solutions and efficiency opportunities of supplying such water needs. However, a widespread reluctance to larger costs associated with water services was also identified, whereby costly alternative solutions were excluded as long-term sustainable from a socio-economic perspective. Due to this, Norrvatten was recommended to continue planning for an expansion of its production capacity, with regard to the conclusion that the identified alternative solutions and efficiency opportunities were not considered sufficient to completely reduce the need for drinking water produced by Norrvatten for garden irrigation and filling of pools. Nevertheless, it was also concluded that the need for expanded capacity could be reduced when implementing the identified solutions and efficiency opportunities. However, the reduced need could not be described in quantitative terms with the chosen methodology. Because of that reason, Norrvatten was recommended to examine this further in future projects considering that it would provide a valuable basis for operation decisions regarding expanded production capacity.

Cape Town, South Africa, falls within a winter rainfall region, making it difficult to assess the feasibility of rain- and stormwater harvesting. The reason for this is because the region’s high water demand period coincides with the low rainfall summer season, thereby limiting the availability of this alternative water resource when most needed. During this study, rainwater harvesting for toilet flushing purposes, collected from roof surfaces, was practically assessed by means of inserted flow meters at a pilot study site in Kommetjie, Cape Town. The combined and single system roof- and land surface runoff yields and savings of commercial buildings within the Kommetjie business area, were also theoretically assessed by making use of a mathematical roof- and land surface runoff model specifically developed during this study. The statistical testing of the hypotheses statements relating to the pre- and post-harvesting savings at the pilot study building, compared against the average actual municipal water usage, were performed. Hypotheses testing were also performed in order to compare the theoretical rain- and stormwater runoff yields for the commercial business area against the average actual municipal water consumption. The conclusions drawn from this study indicated that valuable potable water, as well as related financial savings, can be achieved within a winter rainfall region, thereby making rain- and stormwater harvesting a feasible option for commercial businesses in Cape Town. / Environmental Sciences / M.Sc. (Environmental Management)

Cape Town, South Africa, falls within a winter rainfall region, making it difficult to assess the feasibility of rain- and stormwater harvesting. The reason for this is because the region’s high water demand period coincides with the low rainfall summer season, thereby limiting the availability of this alternative water resource when most needed. During this study, rainwater harvesting for toilet flushing purposes, collected from roof surfaces, was practically assessed by means of inserted flow meters at a pilot study site in Kommetjie, Cape Town. The combined and single system roof- and land surface runoff yields and savings of commercial buildings within the Kommetjie business area, were also theoretically assessed by making use of a mathematical roof- and land surface runoff model specifically developed during this study. The statistical testing of the hypotheses statements relating to the pre- and post-harvesting savings at the pilot study building, compared against the average actual municipal water usage, were performed. Hypotheses testing were also performed in order to compare the theoretical rain- and stormwater runoff yields for the commercial business area against the average actual municipal water consumption. The conclusions drawn from this study indicated that valuable potable water, as well as related financial savings, can be achieved within a winter rainfall region, thereby making rain- and stormwater harvesting a feasible option for commercial businesses in Cape Town. / Environmental Sciences / M.Sc. (Environmental Management)