Water Safety Toolkit for Reopening Buildings

Building Drinking Water Safety After Long Term Closures

The Issue

When buildings are closed or have low occupancy for any prolonged period, water in the building becomes stagnant and can pose serious health risks. The effect of such stagnation will vary between each building based on factors such as length of the shutdown, size of the building, number of occupants, complexity of the system, integrity of the plumbing, and maintenance performed during the shutdown.

Primary Issues with Prolonged Stagnation in Building Plumbing

  • Loss of disinfectant effectiveness within days or weeks
  • Loss of corrosion control effectiveness
  • Changes in water temperature in building services (cold water increase and hot water decrease)

Health-related Risks

  • Growth of pathogens (Legionella pneumophila, non-tuberculous mycobacteria, Pseudomonas aeruginosa, free-living amoeba), and microbial community shifts that can cause serious infections
  • Metals (lead, iron, copper) and/or arsenic leaching from plumbing materials into drinking water
  • Water discoloration, taste and odor
  • Nitrification which further feeds microbial growth
  • Regulated disinfection byproduct concentrations increase


While the City of Hamilton is responsible to get clean, safe drinking water to each property, it is the responsibility of each property owner to ensure it maintains the safety of that water within their buildings

Do you have a plan? Building Water Management Practices to Reduce Water Quality Issues

  1. Building Water Management Plan
    If a Building Water Management Plan is in place, this should include information on management of the water system and should be followed to reduce risk. These will commonly include an overview of the building water system, regular flushing protocols, thermal regulation, and water quality testing.
  2. Periodic flushing
    Replacing stagnant water in the building water system with water from the main will help to prevent water quality deterioration. Flushing locations, frequency and duration should be determined based on the locations of frequent use when the building will reopen, the building and building water system size, and length of the service line to the building.
  • Map or sketch your entire water system
    • Identify zones and include all treatment equipment, pumps, valves, tanks, etc.
    • List all outlets/fixtures such as taps, fountains, showers, eye wash stations etc.
    • Be sure to include any connected food units like ice or coffee makers
    • Large facilities with multiple buildings (like a university campus) should be divided into zones
  • Flush your entire system
    • The purpose of building flushing is to replace all water inside building piping with fresh water
    • Flushing is not one and done - flushing should take place at a minimum weekly from each fixture when occupancy or water usage is considerably lower than normal
    • Staff should wear appropriate PPE (gloves, mask, eye cover) during flushing
    • Minimize water aspiration (breathing in water mist), by removing all aerators and showerheads before flushing
  • Cold Water
    • Flush the cold water system first through all points of use
    • Start where the water enters the building and work from the closest zone to furthest zone and the closest outlet/fixture to furthest outlet/fixture
    • Flush the cold water tap by opening the cold water tap fully
    • Flushing requirements vary but run the water until the water maintains a constant cold temperature
  • Hot Water
    • For flushing the hot water system it is highly recommended that you should drain your hot water tanks and refill
    • Flush the hot water system from closest outlet/fixture to furthest outlet/fixture from the hot water tank until the hot water reaches its maximum temperature through each fixture
    • Flushing requirements vary but run the water until the water maintains a constant hot temperature
  • Cleaning
    • Clean, disinfect and rinse all outlets, fixtures, aerators, screens, showerheads etc.
    • Items containing water filters like some drinking water fountains, fridge water dispensers or other water filters will need to be replaced with a new filter
    • Ensure that cooling towers are maintained (including start-up and shut-down procedures) per manufacturer’s guidelines and industry best practices
    • Regularly flush, clean, and disinfect eye wash stations and safety showers systems according to manufacturers’ specifications
    • Other water-using devices, such as ice machines, may require additional cleaning steps in addition to flushing, such as discarding old ice. Follow water-using device manufacturers’ instructions
    • Clean all decorative water features, such as fountains. After the water feature has been re-filled, measure disinfectant levels to ensure that the water is safe for use
  • Testing
    • For smaller buildings, after flushing, you should be able to feel a consistent cold temperature
    • For larger buildings and any building serving vulnerable populations, testing is highly recommended to ensure chlorine levels are maintained
    • Testing for disinfectant residual - simple equipment and/or testing services are available from local water treatment companies, plumbers and pool professionals
    • Testing for microbial diseases – for complex systems, buildings serving vulnerable populations, or any with a history of contaminations (like Legionella) – these issues are often related to water in HVAC systems. There are products and testing services available – check with your local water treatment company for referral.
  • Continue to Maintain your water system
    • After your water system has returned to normal, ensure that the risk of Legionella bacterial growth is minimized by regularly checking water quality parameters such as temperature, pH, and disinfectant levels
    • Follow your building water management plan, document activities, and promptly intervene when unplanned program deviations arise
  • Sewer Related Concerns from Long Term Building Closures
    • From extended non-use, drains and p-traps can become dry and allow sewer gases to enter
    • Ensure that all toilets have water in their bowls, flush to refill if necessary
    • Floor drain p-traps can often dry out, eliminate sewer gases by simply pouring water down the floor drain

Download a copy of the Water Safety Toolkit for Reopening Buildings (735 PDF, KB)