Assessment of water and residue quality in three different drinking water distribution pipelines within high density areas in Ibadan metropolis, Nigeria

Treated water from the water treatment plant (WTP) gets to the final consumers through complex water distribution systems (WDSs). The study assessed the levels of physico-chemical and microbial qualities of treated water moving through WDSs of different pipe materials and properties of residue deposits on the shallow inner walls of investigated pipes as means of evaluating water and residue qualities. The investigated WDSs include galvanized iron pipes (GIPs), asbestos cement pipes (ACPs) and polyvinylchloride pipes (PVCPs). Assessment of water and residues samples was carried out according to APHA and ASTM standard procedures. Pearson correlation and analysis of variance (ANOVA) were used to evaluate the relationship between two continuous parameters and spatial variability among the investigated pipes, respectively. Results showed that the physico-chemical and microbial instability of water samples were more pronounced in GIPs, followed by ACPs and least in PVCPs. However, changing water quality indicators were found to be significant in water from GIP and ACP of smaller diameters. Most of the drinking water quality parameters in treated water at WTP lie within the standard permissible limits for drinking purpose. However, the water quality deteriorated bacteriologically, from the WTP to the WDSs. The mean pH ranged from 6.9 to 7.5; temperature fluctuated from 30 to 31 °C; EC varied from 147.3 to 248.8 μS/cm while total suspended solids (TSS) varied from 40.6 to 503.8 mg/L. Chloride ions ranged from 102.4 to 355.2 mg/L with its mean values in GIPs and 75 mm diameter ACP above the safe limit for potable water. The redox potential values of < 400 mV in all analyzed water samples indicate enhancing environment for biofilm growth. The results of residue properties further corroborate the level of quality indicators in collected water through the investigated pipes. The overall results indicate that pipe material, pipe diameter, and anthropogenic sources contribute to alteration in water quality of conveyed treated water. The Pearson correlation result shows that most of the analyzed water parameters except resistivity and dissolved oxygen (DO) positively correlate pair-wise either at 1% or 5% levels. The ANOVA indicates that pH and \({\text{HCO}}_{3}^{ - }\) concentrations in water from GIPs were significantly higher at 5% level than those found in water from PVCPs, ACPs and WTP. The oxidation-reduction potential (ORP) of treated water was significantly lower than that of water samples from all the investigated pipes at \(\alpha\) = 0.05. However, the ORP values in residues did not vary significantly among the investigated pipes at 5% level. The study recommends reservoir cleaning program, suitable modification of treatment procedures, and constant check for leakages in the main distribution systems and service pipes among others as means of maintaining the stability of water quality status of treated water through the WDSs.