Small water municipal drinking water systems face special challenges as they have a smaller tax base. This often requires provincial or federal government financial supports through grants or low interest loans. Water cooperatives in rural areas lack direct access to a tax base and so have additional challenges. In Canada, many small systems, both municipal and rural, continue to encounter boil water advisories and even disease outbreaks (Dore, 2015). Hundreds of drinking water advisories are put in place every year across Canada, and the majority of them are issued for systems that serve 500 people or less (Environment and Climate Change Canada, 2018).

With appropriate public funding, many of these problems could be reduced or eliminated. However, typically in North America, each small community must cover its own capital and operating costs of their drinking water supply, although some jurisdictions offer a subsidy for capital costs. Often, a rural community has a small population, lower average income and consequently a lower tax base. These financial constraints as well as other risk factors were highlighted at a 2004 conference on small water systems (Ford et al., 2005).

Some households may be in locations where a water treatment plant has excess capacity to supply additional connections. In such circumstances, small diameter low-pressure supply systems can be connected to major trunk lines to give these households access to water. These typically occur in locations that do not belong to recognized municipal or other local government. A possible solution is to have small diameter low-pressure supply system coupled with decentralized cisterns at the households. Such supply systems called “trickle fill,” have been implemented in South America, in the Pacific islands and also in the province of Alberta, Canada. Trickle fill allows rural households to benefit from the economies of scale of the larger regional water treatment plant while providing a solution to the cost challenges of providing full treatment and traditional municipal style distribution system found in small, rural and First Nation systems.

The word “regionalization” refers to small communities connecting to a nearby larger regional system via a transmission line instead of investing in their own small stand-alone drinking water treatment plants. Regionalization might require upgrades to increase the capacity of the larger regional treatment plant, but adding some additional users are usually possible as the plant capacity is based on the maximum user demand that only occurs a few days in the year, typically in high summer. Regional transmission lines carry the water to the individual communities’ treated  water storage  reservoirs.  

Each community maintains their own existing distribution piping to supply water to their customers.

When transmission lines run past an area with existing rural residential households, it is often feasible to connect to households. In this case, instead of a municipal style service connection, a low-pressure, small diameter or “trickle fill” pipe can be attached so that treated water is delivered to individual customer’s cisterns at each rural property. This method of meeting additional demand is the focus of this paper.

Rural municipalities, new or existing water co-operatives, First Nation communities and private water providers seeking alternatives to their existing water supplies are the primary potential candidates. This applies especially to households that currently truck water in from a distance, or those whose water wells contain high metals (fluoride, arsenic) or otherwise contaminated and not suitable for drinking water.

In this paper, a user-friendly, low-cost decision-making system is proposed to help decision makers assess the economic and technical feasibility of a trickle fill solution for a community, or a group of households. The system, which is presented as a user-friendly Decision-Making Assessment Template (DMAT) is incorporated in a standard spreadsheet application, and can be easily replicated by a community. Hence the DMAT itself is low-cost and requires minimal training; it is available free of charge to potential users.

THE TRICKLE FILL CONCEPT

Rural water supply can be subdivided into two distinct types. One type is where water supply is brought to a small municipality, such as a village or a hamlet, via a regional high pressure transmission line. In this traditional form, small communities connect to a nearby larger regional system instead of investing in their own small stand-alone drinking water treatment plants (Alberta Transportation, 2017). Expansion requires upgrades to a single larger regional treatment plant, which becomes the hub. Then regional transmission lines carry the water to the individual communities’ treated water storage reservoirs. Each community maintains its existing distribution piping to supply water to their customers.

The second type of rural water supply is “trickle fill”, where regional water supply is brought from a transmission line to decentralized cisterns located at the rural homes and institutional/commercial customers in a low population density area via low-pressure, small diameter distribution piping (Figure 1). Trickle fill systems often are built in areas where traditional regional transmission lines exist and are within a reasonable proximity to the area intended to be served.

Examples of trickle fill implementation

Drinking    water     trickle     fill      systems    have    been implemented in many places throughout the province of Alberta, Canada. In approximately 20% (15 out of 72) of the rural counties and districts in Alberta, residents have connected to regional systems by implementing the trickle fill design (Roulston, 2017; Alberta Municipal Affairs, 2017; AUMA, 2018). This trend demonstrates that the trickle fill solution is technically feasible in rural areas, and indicates there is potential for social acceptance of it in the province. It also suggests that there is an existing knowledge base regarding its development and operation.

Figure 2 illustrates the extent of regional water transmission lines. On a provincial map, trickle fill system piping looks like a grid or hub-and-spoke. Figure 3 shows the extent of trickle fill water lines in addition to the regional transmission lines.

There are examples of trickle fill systems elsewhere in Canada as well. The Carlsbad Trickle Fill System supplies an institutional/commercial development in Ottawa, Ontario (Infrastructure Policy Group, 2014). There is a pair of pipeline associations that use trickle fill water supply in Saskatchewan: Melfort Rural Pipeline Association and the Coteau Hills Pipeline Association (University of Saskatchewan, SK Association for Rural Water Pipelines and PFRA, Agriculture and Agri-Food Canada, 2002). Outside of Canada, there are reports of trickle fill systems being constructed in South America, starting in the early 1970s, and in the South Pacific island country of Kiribati in the early 2000s (Albetis and Lenehan 2003). South Africa also has examples of trickle fill systems in use (Scott and Tipping, 2001).

Past practice and the successful implementation of trickle fill in Alberta over the last decade indicates that there are some circumstances when trickle fill solution is suitable. Based on the authors’ analysis and field knowledge of current completed projects, Figure 4 indicates factors that influence whether trickle fill would be a  feasible   option   for   a   rural   service   area.  Past experience suggests that a cluster of water users located within 50 km from a transmission line could consider a trickle fill solution, provided the terrain gradient is appropriate. Greater distances may require a transmission line with a larger diameter pipe and/or higher pressure followed by additional reservoirs.

Those considering trickle fill systems can benefit from the experience of previous projects. Unfortunately, the published literature on this subject is limited. Project outcome or synopsis reports are not available to the public, making it more difficult for potential proponents to be aware of the solution or know how to determine if it would be the right fit for them. Hence, the decision-making template developed in this paper would help those considering the use of trickle fill.

3) Cost component calculations.

4) Normalization and combination of cost components into total dollar cost per month per household.

5) Financial feasibility assessment.

6) Determination of key energy and environment impacts of switching to trickle fill system and the associated change in the carbon footprint.

The scenario development and technical feasibility assessment are the most critical and sometimes most time-consuming elements of the process. These two steps work together to produce the concept design, which will then be tested for financial feasibility. Once a geographical area of interest has been selected, the assessor needs first to decide which type of planning horizon will be used. If a long-term planning horizon is desired, then future growth will need to be considered in the scenario. If a short-term planning horizon is deemed appropriate or minimal growth is anticipated, then only the present-day data on the number of households will be required. The groupings of potential customers and the tie-in point to the existing system should be identified and marked out on a map. The existing system type, number of connections, and number of households for each customer grouping will need to be identified as these characteristics have a bearing on the cost structure and environmental impacts per household. To conceptualize the potential new distribution network, basic preliminary routing principles can be applied. The preliminary routing process should include marking out the potential pipeline routing on a map by following roads, identifying any known existing pipeline right-of-way, and avoiding any obviously complex crossings. Opportunities to use blanket easements on private land should be considered in the routing as previous trickle fill projects have found this an effective way to keep capital costs down (Tiffin, Personal Communication, May 2, 2018).

Langford et al. (2012) outlined an approach for determining the high density polyethylene (HDPE) piping specifications (size and pressure rating). The demand data (that is, population projections, water usage rates, types of demand, major water users, and required delivery pressures) are critical inputs. Primary water consumption data should be used where possible. Best practice recommends that the projection of the water demand on the proposed system should consider “historical data, previous studies, record drawings, digital mapping, public opinions, and application of engineering principles” (Langford et al., 2012, p. 802). As a starting point, the following pipe sizes should be selected: for mainlines that need fire flow, use a minimum diameter of 150 mm (6”); for other mainlines, use a minimum diameter of 50mm (2”).

Once the conceptual piping route has been laid out, its technical feasibility will need to be assessed via hydraulic analysis. Once the scenario has been developed and determined to be technically feasible, the economic analysis part of the process can begin. Cost components to be considered include:

Capital cost: Order of magnitude cost estimates to build the new trickle fill system.

System connection cost: Determined by owner of existing system, and commonly referred to as an offsite levy. This typically captures portion of capital cost of existing infrastructure.

Treated water purchase cost: Determined by owner of existing system. Water treatment costs associated with the water consumed.

O&M cost: Costs of running the existing distribution systems (e.g. water co-op reservoirs) only. Any incremental O&M costs for the new trickle fill piping are assumed to be covered under the water treatment purchase cost.

In  this  framework,  the   capital  cost  is  shared  equally  among “household equivalents” (defined below), meaning that the capital cost amount of the monthly rate for each single-family household is the same. Once the cost components are calculated for each customer grouping, they should be normalized into $/month/ household and then summed together to give the total monthly cost per household within each grouping. Note that the capital cost is a flat rate and does not depend on water usage. For the capital and system costs, an amortization period needs to be determined. To convert the values into per household, institutional and commercial customers will need to be assigned a “household equivalent” (H_eq). This framework recommends using the ratio between the water consumption of the given institutional or commercial customer and the average household consumption to determine H_eq. Averaging the normalized total cost values of all the customer groupings will provide the average total cost per household per month. That value can then be compared against the determined affordability threshold for that population of customers. In the absence of a case-specific affordability threshold, 2% of the province’s median household income (MHI) can be used (Janzen et al., 2016) as an affordability benchmark.

The next step after the economic feasibility assessment is the estimation of key energy and environmental impacts of switching from the existing systems (either trucking in water or drawing from a nearby groundwater well) to the proposed trickle fill system. The DMAT examines the change in three metrics: energy consumed, fossil fuels consumed, and greenhouse gases emitted (EPA, 2018). The “per unit of water delivered” impact metrics are required in order to estimate the change impacts. The difference in energy consumption (MJ/m³), fossil fuel consumption (kg/ m³), and greenhouse gas emissions (kgCO_2eq/m³) are estimated. The change in the carbon footprint is soon likely to become a crucially important consideration in public infrastructure projects, as Canada transitions to net zero carbon to meet its obligations to the global Paris Agreement, 2015, ratified by Canada on October 5, 2016. (Canada, 2016).

Case study area selection

The chosen case  study  area  for  this  project  is  in  the northeast portion of Rocky View County (RVC), Alberta. This area has been chosen for this project for a few notable reasons. First, the case study area is close to an existing regional water system that has capacity to serve additional customers and is owned by the rural municipality. This existing regional water system includes a surface water treatment plant, water pump stations, high-pressure transmission mains, and treated water reservoirs (MPE Engineering Ltd., 2013). Second, data is available for the determination of the system connection and water treatment cost components. Third, residents of the area could see an improvement in their drinking water quality and quantity if they were to switch from their current groundwater supply to the regional supply. Currently, some water systems and individual residents obtain their water by trucking it from neighbouring municipalities. The remaining residents obtain water from individual or communal wells. The groundwater in the eastern portion of rural case study municipality contains elevated concentrations of Total Dissolved Solids (TDS) (Hydrogeological Consultants Ltd., 2002). Groundwater high in TDS is often high in manganese, iron, sulphur and other undesirable constituents that would not be present in the treated surface water from a regional water treatment plant (Health Canada, 2010, 2016b).

Scenario development

The first step in the development of the case study was to determine where the proposed trickle fill system would tie-in to the existing regional system. A tie-in point at an existing pump station and reservoir that was currently being underutilized was selected. The existing pump station was located in the center of the case study area. Connecting  more  users  would  also   have   the  added benefit of improved operational efficiency for the existing station. By increasing the demand on the reservoir, the residence time (and thus the water age risk and associated costs of mitigation) would be reduced.

The second step in the scenario development was to identity the customer groupings to which the new trickle fill system would deliver the water from the regional system. Input was gathered from municipal and regulatory bodies on potential customers within the case study boundary. They identified existing water co-operatives, distribution centers, and other entities that currently truck-in their water or access groundwater wells. These inputs are the starting point for the plan, marking the groupings that they suggested on a map. Then, using Google Maps (satellite view), clusters of homes were identified in the area and are added as groupings to the plan. Future growth or new developments were not incorporated into the DMAT as those would need to be serviced by additional distribution lines. Finally, the scenario assumes a medium-term (about 10 year) planning horizon.

With the groupings and tie-in point identified, the general route for the trickle fill water distribution piping was mapped out. The piping was routed to follow existing roadways and used Google Maps to determine piping lengths. The scenario parameters of population, homes and connections are summarized in Table 1. The proposed trickle fill water distribution network would be installed to deliver water to fifteen discrete customer groupings. There were three distinct customer groupings:

Incorporating economic, energy and environmental impacts

Upfront costs

It was determined that it would cost approximately $6.6 million to design and construct the new trickle fill piping network. Table 2 presents the estimated total upfront costs for the case study scenario. Normalization of the total capital cost value gives $24/month per home equivalent. The sum of all the system connection fees is calculated to be an additional $11.7 million. The system connection charges are nearly double the estimated capital cost of the new trickle fill piping network.

End-user cost

The total end-user cost of water was calculated for each grouping. Each grouping total includes its respective allocated capital, connection fee, water purchase, and, if applicable, distribution system O&M costs. For residential groupings, the end-user costs were found to vary, ranging between $110/month/household to $190/month per household.

The   cost   for    institutional/commercial   connections varied dramatically based on the water usage. The estimated end-user costs ranged from $690/month for a small elementary school, $3 200/month for a large high school, to $22 000/month at a large year-round RV Campground.

Figure 6 provides an illustration of the breakdown of the total cost of water into four cost categories: capital, O&M, water purchase and connection fees. What becomes immediately apparent when examining this breakdown is the fact that the water purchase (or cost of water treatment) is the dominant component (50%). The system connection component comes in second place (28%); the capital cost (or new pipeline construction cost) comes in third (15%); and the distribution system O&M cost comes in fourth (7%). This breakdown emphasizes the impact of the system owner rate schemes on the end-user monthly cost. In RVC’s case, the variable rate of $3.915/m³ is relatively high compared to baseline variable rates of nearby municipalities such as Calgary ($1.67/m³) and Chestermere ($1.33/m³) (Rocky View County, 2018; City of Calgary, 2018; City of Chestermere Council, 2018). This means that a user’s water consumption from the RVC system can significantly impact the total amount they pay for water.

The DMAT presents a low cost, user-friendly method of evaluating an innovative solution that could enable reliable access to high quality drinking water that meets the Canada Drinking water Quality Guidelines for rural water users. The template takes account of economic, energy and environmental factors in assessing whether a trickle fill solution for those water users is viable. If the DMAT makes more than a prima facie case for a trickle fill solution, a full-scale engineering study can then be undertaken.

The application of the DMAT would take into account all the relevant local factors. Not all locations and contexts are suitable for a trickle fill solution. In the case study reported here, it was determined that, while trickle fill is technically feasible, its economic viability depends on the scale of provincial subsidy that could be obtained. 

The case study finds that trickle fill solution would bring about the average cost of water to be $165 per month per household. Comparing this average against 2% of the province’s Median household Income (MHI) of about $156 per month, one can conclude that, without any subsidy, the water users may not support the proposed solution. However, $165 per month per household  is  within the range of what many households may already be paying for their water in this rural municipality. Hence for this particular case study, it may not be surprising if there is little enthusiasm for a trickle fill solution, without a subsidy. If it is assumed that water bills should not be much higher than about 2% of MHI, a subsidy of approximately $1.8 million would be needed to keep the water cost within the affordable range.

Another way to get maximum social value of the existing investment in a regional water supply network may be to provide the required capital funding for the trickle fill solution by the rural municipality that owns and operates the existing water treatment plant and then cover the cost through an increased property tax on the new households that will now receive treated water; such that increase in tax can then be amortized over the next 20 to 25 years. The financial implications of this option, including projected interest rates, merit further study.

Those considering trickle fill solution should investigate the extent that it would reduce the operational complexity and costs at existing water co-operatives as well as at rural institutional/commercial properties.

Trickle fill water supply is also likely to reduce energy consumption and have a smaller carbon footprint. The trickle fill water supply solution is a rural specific approach that shows promise in providing safe, secure and sustainable drinking water supplies to households and other rural institutional water users.

This research was made possible by an NSERC research grant to Gopal Achari. All authors would like to thank the numerous system operators, managers and owners, and operators who assisted in the development of the case study scenario. Additionally, all authors would like to thank two anonymous referees of this journal for helpful comments. However the Authors alone are responsible for any remaining deficiencies.

The authors have not declared any conflict of interests.