## 5 Conclusions  
Meeting community water supply needs within sensitive large African lake settings requires careful consideration. Study of Lake Chilwa Basin's Phalombe District has permitted assessment of groundwater quality constraints upon rural water supply. Furthermore, we have shown that paleo-environments of a previously much larger Lake Chilwa have a significant control on groundwater quality. Lacustrine sediment deposition forming high-level deposits before lake enclosure and lake terraces under both open and closed lake conditions significantly control groundwater major ion quality and salinity observed today. A pivotal finding is the demarcation between low-TDS groundwater suitable for water supply found in basement rock/colluvium uplands, versus higher-TDS, brackish water encountered at the onset of high-level deposits, coincident with the late-Pleistocene maximum lake extent. Increased TDS due to greater residence times and slowing groundwater flows and increased sodium-type waters attributed to lacustrine clay sediment ion exchange is generally found down gradient from the high-level deposit line towards Lake Chilwa. Low-TDS groundwater nearing the lake is limited and where occurring is ascribed to mid-to-low reach influent leakage of low-TDS rivers incising lake terraces. Permeable fluvial deposits at depth within the cross-lake deeper paleo-river channel may offer higher-volume supplies, although water quality there requires verification. These findings underpin a conceptual model that is informed by the influence of the former larger lake Chilwa depositional environment, and which exhibits control on groundwater flows and salinity observed today. The model enables recommendations on delivering increased security of water supply to address significant water point functionality and current asset status concerns quantified at Phalombe District and Basin scales, especially the disproportionate failings of surface water sources. Supply recommendations target not only the various low-TDS groundwater highlighted above, but also the improved use of low-TDS stream/river supplies from basin uplands. Development of fewer, but larger capacity gravity-fed surface water supply schemes is advocated. Larger schemes may overcome maintenance concerns currently causing a multitude of small schemes to fail and also enable aspirations to deliver a SDG 6 'Safely Managed' level of service not achievable with community tap and hand-pumped borehole supplies. IWRM involving both groundwater and surface water sources is hence viewed critical. Although the current take of water for community supply hasincreased by an order of magnitude over the past 30 year generational cycle, it remains a small quantity overall; but is likely to increase further. This needs to be monitored and a sustainable balance struck with other water demands and sensitive lake environment needs amid changing water availability influenced by climate change, especially in the face of increasing agricultural demands. Our multifaceted approach taken to rural water supply science-led policy review is founded on a conceptual model informed by both its paleo-environment and current water flow/quality observations, and further conditioned by current water supply status and functionality assessment, thereby enabling relevant recommendations on water supply. This 'joined-up' approach is one deserving of wider application in countries with similar challenges to those in Malawi.