Methodology used for networks

In order to obtain the investment in renewal for water supply and sanitation networks, firstly, it is necessary not only to know the current redevelopment value that would result from deploying again those same networks, keeping their characteristics intact (as-new replacement value), but also the value that would result from renewing them taking into account current technical criteria (renewal cost).

The following technical criteria were taken into account to calculate this network renewal cost. Firstly, FC pipelines are replaced by PE ones, as recommended by AEAS (2017) regarding the renewal of pipelines. In this regard, it should be noted that, on average, PE is 3% cheaper than FC in relation to water supply, but twice as expensive when talking about sanitation (as can be seen in Appendix D). However, these figures vary according to diameters and population strata.

Secondly, it has been assumed that part of these pipelines is to be renewed using trenchless technology. Specifically, small diameter pipelines are fully renewed using trench digging, since trenchless technology is not usually applied to small diameters. However, medium and large diameter pipelines are renewed partly by digging and partly using trenchless technology. The percentage of trenchless technology use is set at 5% for medium diameters and 10% for larger ones.

In order to obtain trenchless work units prices, various projects using trenchless technologies were analysed (listed in Appendix C), to establish a ratio between the trenchless work unit and the work unit using digging (considered to be the sum of pipeline and civil works prices). The other prices (deployment and accessories) are considered to be similar for both technologies.

Since the number of trenchless technology projects is reduced, the comparison of work units is done nationwide without distinguishing between material type or diameter. Regarding water supply, the trenchless technology price is 1.28 times the price of digging. By contrast, in relation to sanitation, the trenchless technology price is 0.25 times the price of digging. Disparity between these two figures is due to the usual diameters for each process: regarding water supply, diameter ranges are smaller, so that civil works savings are not significant; conversely, concerning sanitation, larger diameters are used, thus trenchless technologies save higher civil works costs.

However, literature has noted that trenchless technologies generally account for a 10-30%

decrease in costs when compared to digging (Arce Obregon, 2016; Najafi and Kim, 2004). Therefore, considering the analysed projects and the content of technical literature, the trenchless work unit regarding water supply is set to be 15% more expensive, while concerning sanitation it is 20% cheaper.

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The renewal cost for water supply and sanitation networks, as detailed in Table 13 is obtained by applying these two criteria (replacing FC with PE and using trenchless technology).

Table 13. Renewal cost of water supply and sanitation networks

(expressed in € millions), broken down by Autonomous Community and population strata

TOTAL WATER SUPPLY NETWORKS SANITATION NETWORKS

Total 166,129 36,572 129,557

In the case of the water supply network, the cost that would result from renewing this network today under current technical criteria is €36,572 million, while the cost of renewing the sanitation one amounts to €129,557 million. It is verified that, in both cases, the cost of renewing the water supply network is slightly higher than its current value (see Table 9). Regarding water supply, this is due to the fact that trenchless technology is more costly than renewal using digging. By contrast, regarding sanitation, trenchless technology is cheaper and the higher cost of renewal is due to the higher price of PE. In any case, the difference between the as-new replacement value and the renewal cost is minor. In addition, it was found that, similarly to the case of the current value, most renewal costs (both regarding water supply and sanitation) are concentrated in those Autonomous Communities and population strata with the highest number of inhabitants.

Once the cost of renewal for water supply and sanitation networks has been obtained, the next step is to calculate the annual cost of renewal, based on information about their renewal period. Specifically, in order to achieve the annual cost of renewal under the baseline scenario, it is necessary to know the renewal period for each network, according to each material type and stratum of the population. This information comes from the “2018 Survey on the condition of water

infrastructures in Spain”, which enquired service providers on network renewal period, broken down by materials and diameters.

On the basis of this information, two complementary procedures were followed in order to calculate renewal periods:

• Technical renewal period according to the survey of service providers.

• Renewal period based on theoretical limits

The first procedure consisted in taking the renewal periods stated in the results of the above survey, ruling some atypical ones, which were extremely reduced. Results obtained using this procedure are shown in Table 14, for each one of the materials used in water supply and sanitation networks, and according to population strata.

Table 14. Renewal period (expressed in years) of each network material, broken down by strata of population, according to the survey of service providers

WATER SUPPLY NETWORK SANITATION NETWORK

FC (renewed Using PE) Ductile

iron Concrete PE PVC Others FC (renewed Using PE) Ductile

iron Concrete PE PVC Others

However, renewal periods obtained in this way, known as “technical renewal period according to the survey of service providers”, result in investment requirementsinvestment needs that are, in some cases, far different from the reality of water supply and sanitation systems and sanitation, and are probably considered impracticable in reality.

With the aim of obtaining a comparative range, a second procedure, called “renewal period based on theoretical limits”, was followed, so that by appropriate technical consultation, this period is defined as the largest one in which water supply and sanitation systems are not unsustainably compromised due to the aging and degradation of infrastructures.

It is important to note that periods obtained in both cases are based on the technical estimate provided by experts in the urban water field, and that a calculation process solely based on the durability and degradation technical criteria for infrastructures was followed, whether real estate or electromechanical or technological equipment. Thus, estimates by other actors that may disturb or alter the estimation of these periods fall outside the scope of this study.

On the other hand, it is also necessary to note that the obtained periods are a statistical approximation based on the responses to the conducted survey and, therefore, these are not the authoritative reflection of any water supply and sanitation system in particular. These periods provide very accurate information on the total average of all infrastructures existing in Spain, as well as its renewal needs, based on these estimated periods.

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However, depending on the service provider and system to be compared to these data, results may be an approximation (close, but not precise). The aforementioned is without prejudice to the establishment of specific renewal periods based on the work of service provider technicians according to their knowledge, experience, inventory, water quality and as many variables to be considered in their corresponding analysis; these periods may be used where appropriate to conduct studies on the investment needs of infrastructures under their management.

Taking these two procedures for obtaining renewal periods into account, subsequently these are applied to the proportion of materials within each Autonomous Community, in order to calculate the average renewal period of water supply and sanitation networks, broken down by population strata and Autonomous Communities.

Using this information, regarding each stratum of population within each Autonomous Community, the renewal cost of each material is divided by the renewal period of such material (expressed in years), to obtain their annual renewal cost, as detailed in Equation (7). The annual cost of total renewal is the sum of the annual renewal costs of all materials.

Finally, in the case of the water conveyance network, in the absence of more accurate information, the process is as follows: regarding each stratum of population within each Autonomous Community, the as-new replacement value of the network has been divided by the average renewal period of the water supply network, to calculate the annual investment in renewal.