We naturally assume that our tap water is safe to drink. Our tap water goes through a treatment process before it gets to our homes to ensure it is fit for consumption. Drinking water in the UK is sourced from reservoirs, aquifers, lakes and rivers. Water then goes through a rigorous set of processes at water treatment works, before being pumped into your home to drink. The treatment process of the water depends on the type and quality of the source. Groundwater treatment works extract water from sources below ground such as springs and aquifers. Surface water treatment works take water from above ground sources like reservoirs and rivers. Water from these above ground sources are exposed to the environment, so go through individual process steps in different combinations to clean and disinfect.

The water treatment process

Abstracted raw water is pumped from its source to the treatment plant for processing. The water that has come from surface sources such as rivers are sometimes held temporarily in large open storage reservoirs; doing this allows the blending of abstracted water with the water already held in the reservoir, which dilutes incoming contaminates. The water can be held in the storage reservoirs for months before it is pumped to the works for treatment. The long storage time will allow for some water quality improvements; some of the bacteria present in the water will die off, the exposure to sunlight will break down any organic material, debris and solid contaminants will settle out. The process of screening is mainly used for surface water sources, and will remove floating objects such as leaves as the water is passed through metal grids and screens. The clarification process will involve adding a chemical coagulant dose into the water; it will bind together fine suspended materials such as silt and mud particles. The coagulant will trap clumps of material, and will then be removed by settlement or flotation.

The filtration stage of the process is achieved by sieving any suspended material from the water. Slow sand filters have a biological action, as the top sand layer trap organic material, and will support the biological growth of any bacteria and microorganisms present. Aeration is then used to remove the level of oxidise; compounds such as hydrogen sulphide and carbon dioxide.

The next stage is Granular Activated Carbon (GAC), this is an advanced system that is used to remove pesticides, unpleasant tastes and odours as well as any present organic compounds. Ozone dosing is an advanced treatment process; this involves injecting ozone into the water to breakdown and pesticides still present. Ozone will attack compounds and destroy them, it is also an anti-bacterial. Chlorine is then added to disinfect the water; it will either be added as a liquid, or a gas. Ammonia can be dosed into the water following final chlorination for a longer lasting disinfectant.

Water quality legislation

UK water companies work under strict legislation and standards set out by UK governments and other regulators like the World Health Organisation. The main areas of legislation are quality, public health, cost and environment. The law requires that our drinking water is clean, wholesome and safe to consume. The clause states that “Water is free from any micro-organisms and parasites and from any substances which, in numbers or concentrations, constitute a potential danger to human health.” Legislation also requires that there is:

• Strict monitoring and analysis
• Public reporting and Data
• Use of treatment chemicals and materials in contact with water
• Action that must be taken if a standard is exceeded

Samples of water will be tested regularly to ensure standards are met. The test will look for any chemicals and contaminants present in the water. The rigorous testing our water goes through is reassuring, as we have confidence in the fact that our water supply is high quality and safe for us to drink.