We received a request through a property management company from the owner of a three-story apartment building in Tokyo, asking us to repair deteriorated piping around the water supply pump unit. As a result of the on-site preview, we confirmed a “cross-connection” in which the pipe before the receiving water tank and the piping after the receiving water tank were directly connected. A cross-connection may cause water quality contamination through backflow and is a connection method prohibited under Japan’s Waterworks Law.

The owner thought, “Even if the pump fails, it is convenient because opening the red valve before the receiving water tank prevents a water outage.” However, based on materials from the Tokyo Waterworks Bureau, we explained the illegality and danger of the connection and proposed switching to a direct pressure water supply system.

A cross-connection refers to a condition in which a water pipe and another piping system are mistakenly connected directly.

• If there is no backflow prevention device during a water outage or similar event, contaminated water may flow back into the water pipes
• As a result, contaminated water may flow into surrounding homes
• Actual cases have been reported in which pesticides or well water flowed back and caused accidents

To protect safe water, Tokyo also conducts ongoing investigations and corrective actions.

This is a method of delivering water directly from the water mains to each unit without using a receiving water tank or pump.

Water Supply Method Conversion Work | Differences Between the Direct Booster Water Supply System and the Direct Pressure Water Supply System

With a receiving water tank system, maintenance and management costs are required to respond to failures and deterioration, such as water supply pump unit replacement (approximately JPY 1.5-2.0 million every 10-15 years) and receiving water tank replacement (approximately JPY 3.0-4.0 million). With a direct pressure water supply system, however, neither the water supply pump unit nor the receiving water tank itself is required.

[Advantages]

• Major cost reductions because water supply pump and receiving water tank renewal costs are no longer required
• Electricity costs previously required to operate the water supply pump are reduced by using pressure from the water mains
• The risk of water outages due to water supply pump failure is eliminated
• Periodic maintenance and management, such as receiving water tank inspection, cleaning, and painting, are also no longer required
• Because water does not pass through a receiving water tank, fresh, safe water can always be supplied from the water mains to each unit
• The site can be used more effectively because space for the receiving water tank is no longer required

Note: As a consideration, water outages may occur during accidents or disasters because there is no storage function.

This work was carried out over approximately two weeks (1/23-2/4).

• Prior confirmation with the waterworks bureau and diameter enlargement work
• Asphalt excavation -> piping renewal and diameter enlargement
• Installation of new valves, check valves, and bypass unit
• Installation of air intake/exhaust valves in each unit (three-story building)
• Removal of the existing receiving water tank and pump unit -> asphalt restoration
• Application to the waterworks bureau

The water outage lasted only one day (9:00-17:00). The impact on residents was kept to a minimum.

• The equipment became simpler, significantly reducing future renewal, maintenance, and management costs
• The safe direct water supply method helped avoid the risk of water quality accidents
• An environment was created in which residents can use the water supply with peace of mind

Although a cross-connection may appear convenient, it is illegal and carries the risk of causing serious water quality accidents. We provide one-stop support, from on-site investigations to optimal proposals based on applicable laws and regulations in Japan. Please feel free to contact us if you are concerned about maintenance and management costs for a receiving water tank or water supply pump, or if you want to improve water quality safety.

Contact us about water supply system conversion work