## 2 Characteristics of Premise Plumbing Systems and Risk of Opportunistic Pathogens
### Expected Changes in Water Quality Resulting from Elevated Water Age
#### 2.2.3 Corrosion Control Effectiveness  
Phosphates are often added to drinking water supplies to minimise the corrosion of piping materials [21; 28; 47]. Increased water age influences the effectiveness of such corrosion control inhibitors by the provision of poorly buffered waters, which challenges pH management [48; 49]. Corrosion can reduce the lifetime of premise plumbing infrastructure and cause leaching of lead and copper into the water [6]. In addition, although there appears to be substantial interplay between corrosion control and disinfection, implications for microbial control are not fully understood.  
Corrosion products react with some disinfectants to enhance or reduce their impact depending on the exact water chemistry and pipe materials [21; 50]. For example, [PERSON] [35] conducted a study showing that metallic pipes (cast iron and stainless steel) consumed more chlorine as they aged, which was likely due to the accumulation of corrosion products. Conversely, plastic pipes (polyvinylchloride and medium-density polyethylene) consumed less chlorine as they aged and exerted no demand after a decade of service.  
'Blue water syndrome' i.e., blue staining occurs in waters with high levels of soluble and/or particulate copper. Although elevated levels of copper in water are not known to cause long-term health effects, it has been linked to gastrointestinal upset and exacerbation of problems associated with nitrate ingestion, especially in children [28]. Such occurrences are expected to be more frequent in certain situations with water conservation practices [21].  
Copper corrosion failure (often referred to as pinhole leaks, and as non-uniform or pitting corrosion) is strongly attributed to frequent stagnation, as well as accumulation of debris during installation, and microbial activity [44; 51]. Therefore, occurrence might be more frequent in green buildings associated with low flow velocities and low water use. Research by [PERSON] and [PERSON] [52] determined free chlorine to be an important factor to induce pitting under certain conditions. Severe pitting corrosion can jeopardise the integrity of an entire plumbing system, for which costs of repair or replacement can be substantial.  
Lead is a neurotoxin that can cause permanent, irreversible damage when consumed and is therefore a recognised threat to public health in water supply [53; 54]. The corrosivity of the supply water is an important driver for lead into building plumbing systems [55]. System design and operation can also influence the rate of release [56]. Prolonged periods of stagnation and high-water age increase the contact time between water and lead-based plumbing components or solders, which can increase the rate of metal release [57]. [PERSON] and [PERSON] [58] observed an exponential increase in lead levels with stagnation time in the first 20-24 h of exposure.  
Lead pipe plumbing is not widespread in Australian homes relative to Europe and the US, where infrastructure is more dated [59]. Nowadays, the installation of lead-based piping and the use of lead-based solders is largely banned for new constructions and renovations. Despite this, the risk of lead exposure remains [60; 61; 62; 63; 64; 65]. A field study by [PERSON] et al. [66] revealed that premise plumbing lines in green buildings with relatively low water demand had very high lead leaching from brass and bronze devices with lead coating.