Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

This is an AMP page - Open full page! for all features.

Cross-Contamination Control

It is fundamental to keep the potable water in the water supply systems uncontaminated

Sponsored Links

It is very important to keep the potable water in the water supply system uncontaminated. A cross-contamination between potentially contaminated water and public water supply systems can occur when the pressure in the supply system is interrupted by a water main break, power failure or some other disruptions in the water service.

When there is a drop in water supply pressure, water can flow back into the public water supply system - so called "back-siphonage" or "backflow". If the backflow water is contaminated, the public water supply system will be contaminated.

Typical sources for cross-contamination:

  • a hose connected to the water supply system is submerged in polluted water
  • a boiler with chemical treated water is connected directly to the water supply system
  • tanks, baths, swimming pools, cooling towers or similar - are connected directly to the water supply system
  • irrigation systems connected to the water supply system

Cross-contamination can be prevented by avoiding direct contact between contaminated water and the water supply by in using

  • vacuum breakers in pipe lines or hoses
  • air gaps between fixtures and potentially contaminated water surfaces
  • check valves

Vacuum Breakers

Back flow of potentially contaminated water to a supply system can occur due to siphoning if the pressure in the system suddenly drops to a lower level. A vacuum breaker installed in the piping or in connection with the hoses will siphon air from the surroundings when pressure drops below atmospheric pressure, preventing contaminants from entering the system.

Air Gaps

A physical separation like an air gap between a fixture and a open water surface in a sink or similar prevents contamination entering the fixture outlet and the water supply system.

The air gap should in general be larger for larger fixtures and closed surfaces (surface with walls) than for smaller fixtures and open surfaces. It is common that

  • the air gap for a fixture of size 1/2" should be at least 1" for an open surface, and at least 1 1/2" for a closed surface.
  • the air gap for a fixture of size 1" should be at least 2" for an open surface, and at least 3" for a closed surface.

Check Valves

A check valve will prevent water from flowing back in the wrong direction.

Sponsored Links

Related Topics

Related Documents

Sponsored Links

Share

Search Engineering ToolBox

  • the most efficient way to navigate the Engineering ToolBox!

SketchUp Extension - Online 3D modeling!

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with the amazing, fun and free SketchUp Make and SketchUp Pro .Add the Engineering ToolBox extension to your SketchUp from the Sketchup Extension Warehouse!

Privacy

We don't collect information from our users. Only emails and answers are saved in our archive. Cookies are only used in the browser to improve user experience.

Some of our calculators and applications let you save application data to your local computer. These applications will - due to browser restrictions - send data between your browser and our server. We don't save this data.

Google use cookies for serving our ads and handling visitor statistics. Please read Google Privacy & Terms for more information about how you can control adserving and the information collected.

AddThis use cookies for handling links to social media. Please read AddThis Privacy for more information.

Topics

Unit Converters

Temperature

oC
oF


Load Calculator!

Length

m
km
in
ft
yards
miles
naut miles


Load Calculator!

Area

m2
km2
in2
ft2
miles2
acres


Load Calculator!

Volume

m3
liters
in3
ft3
us gal


Load Calculator!

Weight

kgf
N
lbf


Load Calculator!

Velocity

m/s
km/h
ft/min
ft/s
mph
knots


Load Calculator!

Pressure

Pa (N/m2)
bar
mm H2O
kg/cm2
psi
inches H2O


Load Calculator!

Flow

m3/s
m3/h
US gpm
cfm


Load Calculator!

10 11

This website use cookies. By continuing to browse you are agreeing to our use of cookies! Learn more