Lesson 21 of 21
In Progress

Water Regulations

NAC-Trainer March 16, 2021


WRAS, which stands for Water Regulations Advisory Scheme, is a certification mark that demonstrates that an item or package complies with the high standards set out by water regulations. 

The installation and use of washing machines and dishwashers in premises connected to the public water supply are subject to the Water Supply (Water Fittings) Regulations 1999 in England and Wales and the technically identical Byelaws 2000 in Scotland. 

The water regulations say all appliances require adequate backflow protection to prevent contamination of the pipework supplying them. To help understand this they have broken it down into five sections (known as fluid categories). 

  • Fluid category 1 – Is wholesome clean drinking water supplied to the property by the relevant utility company for that area. 
  • Fluid category 2 – This starts as category 1 water that has then been impaired by a change in temperature or has been contaminated by the presence of organisms causing a change in taste, odour, or appearance. This would typically be a hot water system in a property. 
  • Fluid category 3 – Is water that might represent a slight health hazard due to the presence of chemical additives. This category typically applies to the water that is contaminated by the detergents used by domestic washers and dishwashers. 
  • Fluid category 4 – Is water that represents a significant health hazard due to the presence of toxic substances such as carcinogenic chemicals and pesticides. This category typically applies to commercial washers and dishwashers used in the hospitality sector. 
  • Fluid category 5 – Is water that represents a serious health hazard because of the concentration of pathogenic organisms, radioactive or very toxic substances, including any fluid which contains faecal matter, human waste, butchery or other animal waste. This is typically waste water. 

Put simply any water from categories 2 – 5 are not allowed to backflow and contaminate water classified as category 1 which is clean safe drinking water. Luckily for us, domestic washers and dishwashers have an air brake system built into the design of the appliance in the form of a dispenser on a washing machine and an air brake/metering tank on a dishwasher. 

These devices allow the water to be gravity fed into the machine which means it is impossible for the water to backflow and contaminate the drinking water. In the event of a backflow scenario the water would just flow out onto the customer’s floor which is definitely an inconvenience but I am sure we can all agree this is preferable to it contaminating the drinking water. 

Waste water 

There are two types of drainage systems found in all properties and homes. Drains for rain water and drains for waste water. 

  • Drains for rain water – This drain collects rainwater from drives, roofs, and roads and it is important to note that it is untreated, it is also described as ‘storm water’. As it is untreated, it is safe to allow it to drain directly into rivers and beaches. 
  • Drains for waste water – This drain takes the foul water to the local wastewater treatment works and accounts for waste generated by toilets, sinks, baths, showers, washing machines, and dishwashers. This waste water covers fluid categories 3 –5 and as its contaminated water that needs treating it is not allowed to flow into the rain water drain. 

If untreated waste water is allowed to flow into the rain water drain then it will pollute the local rivers and waterways and may incur large fines from the Environment Agency. It is important to note that the homeowner or landlord is responsible for making sure they have the correct drain system for the correct type of water. 


Both washing machines and dishwashers require a mains water feed that is taken from fluid category 1 water supplied to the property. As we discussed earlier both of these domestic appliances have an air brake system to prevent backfill.

Domestic washers and dishwashers require a water pressure anywhere from 0.5 Bar up to 8 Bar for them to function correctly. Most homes would average around 3 – 4 Bar and would not experience any fill related problems.  

If the water pressure is below 0.5 Bar, then the customer may experience what we call “Time out Faults” which is when the electronic controls recognize it has taken too long to fill and will stop operation and will then usually display a fault code.  

Low water pressure could also cause inlet solenoid valves not to shut off properly and may result in the drum or tank filling up with the appliance switched off, also as inlet solenoid valves are not meant to be on for long periods of time it could cause them to overheat and fail prematurely, this can be proved with a multimeter looking for around 3 – 5 Kohms and by visually inspecting for heat damage. 

Consequently, water pressure above 8 Bar may cause the pipes, solenoid valves and any fittings to physically break or rupture, this damage would usually be obvious to a visual inspection. 

For suspected water pressure issues, we can test the pressure with a tool shown in the image below. 

Water Fill  

During installation it is recommended that the water tap is within 120cm of the rear of the appliance so that the included water pipe can reach, extra-long hoses are available separately in case the installation is not straightforward. 

See the image below for a good example of the preferred orientation of a water tap. 

The reason we say this is the preferred orientation is to enable electrical and mechanical aqua stops to function as designed (more on this later). Strictly speaking, a standard fill hose will work in any orientation. 

Waste water 

There are generally two ways to set up a drain pipe from a washer or a dishwasher.  

The first would be to use what is known as a standpipe and is shown in the image above, with this setup it is important to make sure the standpipe is approximately 65cm from the floor and approximately 5cm in diameter, it is important to make sure the end of the drain pipe doesn’t go all the way down the standpipe and end up being submerged in water, as this would create a siphoning effect which will possibly cause draining, spinning faults and may even siphon waste water back into the appliance.  

The second way of connecting a drainpipe is to attach it directly to the drain assembly of the sink via a spigot as shown in the image below. 

With this setup, it is important to make sure that the spigot is pointing upwards and that the machine drain hose is higher than the outlet for the drain. Doing this will prevent the siphoning effect from pulling water out of the drain and back into the washer/dishwasher. It will also prevent water from going into the machine when the customer empties the sink.

A common cause for complaint with this setup would be the machine not draining because the spigot is blocked, this is usually caused by the customer pouring things like cooking fat down the sink. Also, with a new install, these spigots are capped off and customers do not realise this which prevents the washer/dishwasher from draining. 

The image below shows a typical plumbing installation that you might find in a customers house!

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