Materials and Products in Contact with Potable Water
The following regulations apply to the approval of substances and products used in the provision of public water supplies within the United Kingdom:
a) England - Regulation 31 of The Water Supply (Water Quality) Regulations 2000
b) Wales – Regulation 31 of The Water Supply (Water Quality) Regulations 2001
c) Scotland – Regulation 27 of The Water Supply (Water Quality) (Scotland) Regulations 2001
d) Northern Ireland – Regulation 30 of The Water Supply (Water Quality) (Amendment) Regulations (Northern Ireland) 2009
DWI Regulation 31 (27 in Scotland and 30 in Northern Ireland) ensures that water suppliers, when producing and distributing drinking water, only use products and substances to that do not cause any detrimental effects on the safety or quality of the drinking water.
Regulation 31also requires that a list of all the substances and products approved or refused under Regulation 31and all approvals revoked or modified shall be published, at least once a year. The latest version is available from the DWI-Defra website below. The list applies throughout the United Kingdom and any product that is listed on it can be used anywhere in the UK.
On a yearly basis the Scottish Government also publishes a list. This can be found on their website: https://www.scotland.gov.uk/Publications/
In addition the DWI has established a list of certain types of products with a small surface area in contact with water that therefore do not require full DWI Approval under Regulation 31 and these require more limited, but specific testing according to their nature and use. These are then classified as being Products permitted to be used under Regulation 31(4)(b) - products with a small surface area in contact with water. Typical examples include joint sealants, anchors and crack injection materials for example; full information on these exceptions is available from the DWI: https://dwi.defra.gov.uk/drinking-water-products/advice-and-approval/Advicesheet8.pdf
All of NCC’s specialists are fully aware of all of these regulations
and the product requirements for use in contact with potable water from source through to delivery and storage in your homes and businesses. For FREE Expert advice
on the selection and use of the most appropriate products and systems for use to protect, or repair and protect your drinking water treatment and storage facilities, please call any of our offices and one of our specialists will be happy to assist you
Drinking Water Sources in the UK
In the UK we get our drinking water from two types of sources. About three quarters of our supplies are from ‘surface water’ i.e. from rivers and the rest is taken from ‘groundwater’ sources.
This water is taken from its source and pumped to open storage reservoirs and then it goes through a rigorous set of processes at our water treatment works before being pumped into the distribution and supply network to our homes and businesses. These treatment processes vary according to the source and quality of the source of water.
Surface Water Treatment Works
These works take their water from above ground sources such as rivers and reservoirs. Raw water from these sources is open to direct environmental input, and multiple treatment steps are required to clean the water and therefore it is pumped from its source to a storage reservoir and then a water treatment plant.
Ground Water Treatment Works
These works abstract water from below ground sources such as aquifers and springs, where it has been filtered over time through permeable rock, gravel and sands etc. As a result, groundwater generally tends to be relatively clean in comparison to surface water, and therefore fewer treatment steps and processes can be required to make it safe to drink.
The Drinking Water Treatment Process
The information below summarises the different stages of the water treatment process and the structures they consist of or are contained in, together with the typical protection that is required for these structures.
The raw water abstracted from surface sources or the ground is temporarily held in large, open storage reservoirs, which allow the blending of the raw water with water already held in the reservoir, which permits dilution of any incoming contaminants. Surface water from river sources particularly, may be passed through a screening process to remove larger materials such as plants and leaves or twigs etc. The water can be held in these storage reservoirs for several months before it is pumped to the works for treatment and this extended storage time already leads to some water quality improvements because:
- Debris and solid contaminants settle-out
- Sunlight breaks down organic material
- Some bacteria will die off
However there can also be some additional contamination if the open storage reservoir is not properly managed, including:
- toxins from algal blooms (when algae multiply at an excessive rate and then die and putrefy in large volumes)
- fouling by birds and animals
- run off of agricultural pesticides or fertilisers
Therefore the water from the storage reservoirs must be further processed and treated before it can be classed as ‘potable’, which means that it is safe for people to drink.
The structures and equipment used to extract, abstract and pump the water into and out of these storage reservoirs do not normally need and particular protection against pollutants and chemicals, but obviously they need to be watertight and the concrete must protect the embedded steel reinforcement from corrosion, or the surfaces can be coated to increase this protection – typically watertight polymer modified cement based mortars (e.g. SikaTop Seal-107), or solvent-free epoxy coatings (e.g. Sikagard 62) are used for this purpose.. Additionally, in some places the raw water can also be very abrasive due to the particles carried in it and the speed at which it is pumped; these areas can be given additional scour and erosion protection.
When the raw water is required for use it is first pumped to a water treatment works to ensure that it comples with the DWI Regulations for our drinking water.
Water Treatment Plants
Each water treatment works is tailored with different processes according to its incoming raw water quality and condition. These processes require some specific water retaining structures and these require varying levels of protection according to the chemical and biological processes in each, together with the thermal and mechanical abrasion and erosion that is also involved. NCC specialists have many years of experience with ‘clean’ water and can advise on specific systems to protect every area of your water treatment facilities.
Typically within most water treatment plants in the UK there are the following processes and structures involved:
These are usually open ‘settlement’ or ‘flotation’ tanks according to the type of particles to be removed. In the clarification process a chemical ‘coagulant’ is dosed into the water, and this acts to bind together the fine suspended materials such as silt and mud particles.
This coagulant forms a 'floc', as the fine particles bind together in larger clumps, which traps the particles and they are removed from the water by settlement or flotation.
There are several different types of filter used in the water industry today and they all function in a similar way; by sieving any suspended materials from the water.
Slow sand filters also have a biological action, as the top sand layers trap organic material, and then support the biological growth of bacteria and other micro-organisms. These micro-organisms breakdown organic compounds held within the water as it trickles through the filter layers, thereby providing an additional cleaning action.
This process can be used to remove, or reduce the level of or oxidise unwanted dissolved compounds such as hydrogen sulphide and carbon dioxide, or dissolved metals such as iron in order to ease their subsequent removal.
Various chemical techniques are used to achieve this removal and the main ones involved today are:
- Granular Activated Carbon (GAC):-
This process is an advanced system used to remove pesticides, organic compounds and unpleasant tastes and odours. The water is directed into GAC vessels, which contain highly porous activated (highly adsorbent of chemical ions) carbon particles, which are able to adsorb the organic compounds from the water, thus improving its quality.
- Ozone Dosing:-
This is a relatively modern water treatment process, which involves injecting ozone into the water to aggressively breakdown pesticides and organic material, because ozone is a very reactive molecule that attacks these compounds and destroys them, by breaking them down into harmless components or easily removed solids. Ozone also has an effective anti-bacterial action.
Chlorine is generally used as the disinfectant and can be added to the water as either a liquid or a gas. It can be dosed immediately into the incoming raw water at the water treatment works to benefit the downstream treatment processes and it will also oxidise unwanted chemicals in the water and have an immediate anti-bacterial effect.
Chlorine is also dosed into the cleaned water at the end of the treatment process, immediately before the water is pumped into the supply network, where it kills any harmful micro-organisms in the water or within the supply network structure.
The final chlorine disinfection process is performed in specially designed closed contact tanks, which are designed to ensure that the chlorine remains in contact with the water for a set amount of time, to ensure effective disinfection. These tanks can be made from steel or more commonly reinforced concrete, both of which require effective protection against the risk of corrosion that can be accelerated by the chlorine in the water.
Ammonia can also be dosed into the water following its final chlorination to form a longer lasting disinfectant, as the ammonia reacts with chlorine to form chloramines, which decay at a slower rate than free chlorine.
This additional disinfection treatment can be useful if the water has to travel large distances, however, chloramines are less effective disinfectants, so it is important to disinfect the water with free chlorine first, before converting the remainder into chloramines.
Advice on the Repair and Protection of Water Treatment Plants
Effective water treatment is essential for protecting public health and effective protection of drinking water treatment and storage facilities is essential to ensure the processes are safely and reliably carried out.
NCC are experts
in the repair and protection of drinking water facilities and can advise on all of the correct procedures, then supply the right materials to carry out the works, with the necessary DWI Approvals for Potable Water Contact.
For advice on finding and selecting the right solution for the protection of your drinking water tanks and other special water processing structures for your project - please call any of our offices and one of our specialists will be pleased to assist you