## 3 Results
### Groundwater Quality Compliance with Regulatory Standards  
Groundwater compliance with Malawi water quality criteria is summarised in Table 1. The relevant regulatory standard is the Malawi Standard MS733:2005 'Standard for water delivered from Boreholes and Protected Shallow Wells' [59] for which 'Maximum Permissible Levels' (MPLs) are set although individual MPLs are not indicated to have a health or aesthetic (e.g., taste, colour) basis. MPLs are exceeded by just 4% of samples for TDS and EC and by 9% for calcium and 1% for sodium and chloride. Although compliance appears good, these standards are quite generous compared to other criteria. Comparison with upper limits of the Malawi Standard MS 214:2013 (for \"Drinking Water Specification for treated drinking tap water\") show an increased percentage exceeding these more stringent criteria. This standard _'does not apply to borehole water, bottled water and natural mineral water'_[60]. Notable exceedances are TDS at 55% (with EC at 23%) and sodium at 46%, iron at 52%, with some breaching by all determinants except for nitrate. Justification for a lower standard is that many water points are directly used for drinking water supply without treatment. However, there is a need for revision of MS214:2013 by the Gov't of Malawi in line with SDG6 target setting objectives. Figure 11: Plot of Basin ground elevation versus Phalombe District observed TDS for groundwater, surface water and Lake Chilwa samples. None of the samples exceeded the WHO guideline values for drinking water health-based criteria (Table 1) [61]. The WHO, however, recognises elevated concentrations for some determinants may affect the acceptability of drinking water [61], for instance drinking water of good palatability with \(\text{TDS}<600\) mg/L is only experienced by 54%. Water is deemed increasingly unpalatable at \(\text{TDS}>1000\) mg/L, 22% of samples (Table 1) and may well account for some of the community water quality concerns (Figure S12, discussed below). Salty tastes due to sodium contents are less at 7% (recognising taste thresholds depend on associated anions and water temperature). Just over half the samples exceeded the iron WHO 'nuisance' threshold of 0.3 mg/L but were all below the Malawi guideline for groundwater supply of 3 mg/L (Table 1). Highest iron predominantly occurs surrounding mountainous area to the east of the study area near to the Mpoto lagoon and approaching Lake Chilwa (Figure S13). Iron results are not pursued herein due to needs for further sampling confirmation and gathering of data to assess redox and electron donor conditions driving iron dissolution from sediments and the possible impacts of different water types mixing in the borehole and the influence of handpump operations oxygenating the samples. There is a need for further study to differentiate iron arising from geological sediments versus corrosion of steel borehole construction materials [57]. Iron is not an uncommon problem in finer grained lacustrine layered settings where semi-confined or confined conditions may sometimes promote iron dissolution into groundwater (higher occurrences are close to, but either side of the high-level deposits boundary line (Figure S12). The occurrence of mWater survey questionnaire 'poor water quality' boreholes reported by communities is compared to our groundwater TDS spatial data in Figure S12 and dissolved iron in Figure S13. The rationale is, in the absence of laboratory analysis, reported problems could relate to taste-impacting high salt contents or visible iron problems. This is partly corroborated by the comparison where higher TDS or iron do coincide with reported poor water quality. For instance, elevated iron predominantly towards the east could account for problems where salinity is unlikely. Some reported problem areas though appear to coincide with neither.