_Applied_  
_sciences_  
Palao-Geohydroology of Lake Chilwa, Malawi is the Source of Localised Groundwater Salinity and Rural Water Supply Challenges  
**[PERSON] 1,*(r), [PERSON] 1,2, [PERSON] 1,3, [PERSON] 4(r), [PERSON] 4, [PERSON] 1, [PERSON] 1(r), [PERSON] 1,5, [PERSON] 6, [PERSON] 7, [PERSON] 4, [PERSON] 1(r), [PERSON] 8, [PERSON] 9 and [PERSON] 1(r)**  
1 Department of Civil and Environmental Engineering, University of Strathclyde, Glasgow G1 1 XJ, UK; [EMAIL_ADDRESS] (S.S.); [EMAIL_ADDRESS] (L.J.); [EMAIL_ADDRESS] (D.J.C.R.); [EMAIL_ADDRESS] (L.H.); [EMAIL_ADDRESS] (A.V.M.M.); [EMAIL_ADDRESS] (M.J.A.); [PERSON]SS] (R.M.K.)  
2 WYG Environmental and Planning (Northern Ireland) Limited, 1 Locksley Business Park, Montgomery Road, Belfast BT6 9 UP, UK  
3 Atkins Limited, Nova North, 11 Bressenden Place, Westminster, London SW1E 5 BY, UK  
4 Ministry of Irrigation and Water Development, Water Resources Department, Private Bag 390, Lilongwe 3, Malawi; [EMAIL_ADDRESS] (L.C.B.); [EMAIL_ADDRESS] (G.J.W.); [EMAIL_ADDRESS] (C.M.)  
5 Stantec UK Limited, 9 George Square, Glasgow G2 1 DY, UK  
6 Department of Civil Engineering, University of Malawi-The Polytechnic, P/B 303 Blantyre 3, Malawi; [EMAIL_ADDRESS]  
7 District Water Development Office Chikwawa District Council, Private Bag 1, Chikwawa, Malawi; [EMAIL_ADDRESS]  
8 District Water Development Office, Phalombe District Council, P/Bag 32, Phalombe, Malawi; [EMAIL_ADDRESS]  
9 Public Weather Services, Department of Climate Change and Meteorological Services, P. O. Box 1808 Blantyre, Malawi; [EMAIL_ADDRESS]  
* Correspondence: [EMAIL_ADDRESS]  
Received: 9 July 2020; Accepted: 29 September 2020; Published: 2 October 2020  
Featured Application: This multifaceted approach to science-led rural water supply policy development for Malawi's Lake Chilwa Basin is founded on a conceptual model informed by its paleo-environment and monitoring of its current water flow/quality. It is conditioned by a recent water supply functionality assessment enabling policy relevant recommendations for sustainable water resource management. The approach is deserving of wider application in similar settings across the developing world.  
Meeting long-term rural community water supply needs requires diligent geohydrorological conceptualisation. Study of Malawi's Lake Chilwa Basin, including sampling of 330 water points in Phalombe District, enabled assessment of groundwater quality influence upon supply. The control of larger Lake Chilwa paleo-environments on current Basin groundwater quality is demonstrated. Lacustrine sediment deposition forming high-level deposits under open lake conditions and terrace deposits under open and closed lake conditions significantly control the groundwater major-ion quality and salinity now observed. Paleo-lake extent marks the transition between low-TDS (total dissolved solids) groundwater suitable for water supply at higher elevations and high-TDS brackish groundwater in areas overlain by lacustrine deposits closer to the current lake level. Low-TDS groundwater is limited to mid-to-low reach influent leakage of rivers incising terraces. Permeable fluvial deposits within the deeper paleo-river channel may possibly provide low-TDS water. The conceptual model,whereby paleo-lake controls groundwater salinity, provides science-based evidence to address policy to manage the significant water point functionality concerns quantified at the district and river basin scales. Targeting of the low-TDS groundwater alongside improved use of upland low-TDS stream/river sources with fewer, but larger capacity, and better maintained gravity-fed supply schemes are recommended. This study hence shows the value of paleo-geohydroology interpretation of the lake-groundwater system conceptualisation to inform Sustainable Development Goal 6 (SDG 6.5.1)--integrated water resources management policy for rural water supply.  
groundwater; Lake Chilwa; rural water supply; Sustainable Development Goal 6 (SDG 6); conceptual model; paleo-environment; functionality; salinity; Malawi