The water quality of secondary water supply facilities is one of the main causes of water quality pollution. Strengthening the control of secondary water supply and guaranteeing the use of water in accordance with the national water quality standards has become a real problem for relevant departments and units to face and solve. The causes of secondary water supply pollution are multifaceted, which is related to the nature of water itself and the cross-section nature of the contact with water. At the same time, it is affected by many external conditions.

The five main causes of water quality pollution in secondary water supply:

1、Pollution caused by secondary water supply network

For without coating line or aging of metal pipes, fittings and other secondary water supply facilities, water consumption is small, pipeline operation at night under the condition of low velocity, pipe wall thick rust scale, will be produced when people open the faucet "including" phenomenon occurs in the morning, this is due to corrosion in water flow speed, water pressure suddenly got bigger, the water quality deterioration caused by washed away a short time. On the other hand, because some of the old residential areas are buried under underground pipeline aging, groundwater and soil and other external materials are easy to infiltrate, resulting in water pollution.

2、Pollution caused by secondary pressurization of water storage facilities

Most of the second pressurized water supply, through the water pool and water tank to meet life, guarantee continuous uninterrupted water supply, water, water tank material is qualified, size and proportion of water consumption is reasonable will affect the water quality. Tank and tank volume is according to the variation of water inflow and water consumption curve calculated and determined, when the lack of relevant data, in terms of guaranteed water, secondary pressure water supply system in the design will be big volume design, thus causing the residence time of water in the pool and water tank growth, decomposition of residual chlorine in the tap water if disappeared, indicators, such as bacteria, total coliforms, will significantly increased, leading to declining water quality.

3、Microbial reproduction pollutes water quality

The types of microbial contamination in the pipes and pools in the secondary water supply facilities usually have bacteria, escherichia coli, autotrophic iron bacteria and the transformation bacteria of sulphur. The main reason for the propagation of these microorganisms is the excessive consumption of residual or reducing secondary pollutants in the water. In addition, if the water retention time is too long, microorganisms in the organic matter in the water again for energy metabolism, reproduction, its products, in turn, will promote the deterioration of the metal surface, cause corrosion to the pipelines.

4、Water pollution caused by external environment

The secondary water supply system can be polluted by foreign countries, causing the water quality to be periodically or sudden. Such as secondary water supply pipeline detonation tube, transformation and other process control poor result in the outside pollution enter.

5、Water pollution caused by poor management

Secondary of pressurized water supply, the urban water supply water quality management regulations, points out that the secondary water supply management unit shall establish quality management system, equipped with specialized professional (is), routine tests on a regular basis, and the cleaning and disinfection of the various types of water storage facilities shall not be less than once every six months. But due to some caused by poor management unit tank (tank), untight seal not regular pool (tank), and other facilities for disinfection cleaning and disinfection is not complete, and so on and so forth, will directly affect the water quality safety. Therefore, the industry suggests that the secondary water supply management unit should fully consider the safety of water supply and avoid pollution of water quality during the implementation of the second pressurization water supply management.