A critical decision to make when planning a water treatment system is whether it will be a centralized or decentralized system.
Under BC's Drinking Water Protection Regulation, small water systems have the option to use centralized or decentralized systems. However, to have a sustainable water treatment system suitable to your situation, it is important to assess both alternatives, based on the need to produce acceptable finished water quality at the most attractive overall cost. In general, the choice depends on source water quality, water demand, treatment targets, capital and operating costs, operator capability, and long-term operating and maintenance costs.
As each water source is unique, the selection of a system to meet particular treatment objectives should be evaluated on a case-by-case basis, taking these factors, among others, into account. Water suppliers are encouraged to consult with the local Environmental Health Officer and the Regional Public Health Engineer to determine an appropriate treatment process.
A centralized water treatment approach, also known as conventional treatment, uses a combined process of coagulation, flocculation, sedimentation, filtration, and disinfection. It treats water in a central location and then distributes water via dedicated distribution networks.
In urban areas, a centralized water treatment system can treat large volumes of water at high rates to accommodate all residential, business, and industrial uses. This approach is well developed and can effectively remove practically any range of raw water turbidity along with harmful pathogens, including bacteria, virus, and protozoa.
However, the capital cost and operating and maintenance costs for a centralized system can be significant. It consists of water source development, construction of significant infrastructures (e.g., the treatment facility, reservoir, and water distribution main), implementation of automated monitor and control systems, and on-site operators.
Smaller communities can reduce costs by using a “package plant”, where treatment units are preassembled in a factory, skid mounted, transported to the site, and virtually ready to operate. However, even then a centralized treatment system may be still financially out of reach for some underdeveloped communities.
Where a centralized community treatment system is unavailable or unaffordable, a decentralized system – point-of-entry (POE) or point-of-use (POU) – installed at the individual home or business can be used to achieve potable water. POEs treat the raw water before it enters the property or home, while POUs are installed to treat water where needed, such as at kitchen and bathroom taps.
In underdeveloped areas, where there are significant deficiencies in financial resources and technical supports, POEs/POUs may be the only treatment option. Although POEs/POUs are inexpensive relative to centralized systems, because they defer large initial capital investments and reduce operating and maintenance costs, they are limited by their treatment capacity and capability for dealing with multiple contaminates. They also require full community buy-in and monitoring.