Turbid water is opaque or cloudy. It's caused by the presence of materials like silt, clay, and algae. Turbidity level is measured using a nephelometer, which shines light through the water to analyse the amount of light scattered by sediment.
The water in a muddy puddle is turbid, whereas the water you pour into a glass from your kitchen tap isn’t. At least, it shouldn’t be.
If turbid water makes it into the municipal water supply and reaches homes, it can cause problems. The majority of the suspended materials that cause turbidity aren't dangerous, but there's a small possibility of cryptosporidium or similar also being present, which can cause illness.
It’s also a shock for households accustomed to clear mains water, leading to complaints and distrust.
What is water turbidity?
Turbidity is a critical control for water treatment and disinfection, so managing it is a priority for drinking water suppliers. Turbid water also affects the efficiency of UV systems used to 'sterilise' water and remove harmful microorganisms, which is one of the main reasons why regulators set turbidity limits.
The European Water Quality Directives, World Health Organisation, and Drinking Water Inspectorate all specify what’s required to supply safe water, and turbidity is typically required to be <1 NTU (Nephelometric Turbidity Units) at distribution. However, recent amendments to the EU directive recommend aiming for an NTU of 0.3% to guarantee trouble-free disinfection at water treatment facilities.
To achieve this, water is filtered to remove sediment and restore lost clarity.
What causes high turbidity?
Turbidity can be caused by:
- Storms
Heavy rainfall during storms causes earth and other organic materials to flow into rivers, changing the colour and contents of the water. As rivers also flow faster during turbulent weather, particles from the riverbed are stirred up into the water as well.
- Boreholes
When water is taken from an aquifer via a borehole, materials from the ground like chalk, sand, and gravel are present. This can get into the water, especially with new boreholes or reinstated boreholes.
- Pipe maintenance and repair
When water companies work on their infrastructure, the movement of existing pipework can dislodge sediment, discolour the water, and cause sediment to enter the water supply.
- Infrastructure groundworks
Any work to utility networks whether it’s a gas network provider or broadband etc., can disrupt nearby mains and cause turbidity.
Water turbidity filter challenges
Many challenges can arise when filtering turbid water. Some key ones to keep in mind are:
- Oversized or undersized systems
Sometimes off-the-shelf filter solutions are too big. They aren’t practical at filtration sites with limited space and access, meaning standard solutions just don’t fit. In these cases, specialist, contained units offer an alternative and smaller solution with the same reliable performance. Systems can also be undersized – if too few cartridges are used for the process flow rate, the life of the system will be shorter and less economical than a properly sized solution.
- Inappropriate flow rate
It’s important to set the water turbidity filter to the right flow rate so it removes particulate effectively. If the flow rate is too high it could overload the filter, meaning it blocks prematurely and doesn’t filter the water properly, leaving you with the expense of early filter replacement and water that doesn’t meet quality standards. If this is happening, a lower flow rate or two-step filtration for turbidity will help.
- Accurate micron ratings
There are two types of micron ratings – absolute and nominal. Absolute filters will stop 99.9% of the particles that are the same size or bigger than the micron rating. Nominal filters have a percentage rating, meaning they stop most particles that are the same size or bigger than the micron rating – this is usually around 85%. Both have their uses, but in water filtration for public consumption, it’s important to know that the filter you’re using will filter out all particles necessary.
- Poor density
Filters in water systems need to be designed for longevity. This means using filters with graded density to maximise dirt-holding capacity and increase efficiency.
These can be short- or long-term issues. For example, a broken pipe caused by an infrastructure project can appear out of nowhere and requires a rapid response. In situations like this, filter skid systems are the ideal solution. As a rental solution, you can deploy them at the exact location quickly and easily. For longer-term problems, we recommend a containerised system.
What type of water turbidity filter works well?
An absolute rated depth filter is a good option. These types of cartridges can hold a lot of dirt and have extremely low clean pressure losses.
Finding the right water turbidity filter solution
Here are our top tips for finding the right partner and filtration solutions that work best for your needs, processes, and existing infrastructure.
- Talk to multiple suppliers and consider a bespoke solution
An off-the-shelf product will rarely offer the best performance and value for money in the long run, so factor in a little time for suppliers to assess your process and come up with a bespoke solution if necessary. If a supplier can’t offer this, it indicates they may not have the right knowledge and skills to help you.
- Look for quick and valuable responses
In situations where you must be more reactive than proactive, your filtration partner should respond quickly with a good solution. For example, if a new borehole is causing turbidity in the water supply, make sure your supplier can install common connection valves into existing pipework with mobile filtration equipment to quickly address the issue. You should be able to count on them to respond quickly to emergencies with a solution that will solve the problem
- Check products are properly tested and approved
It’s important to choose a supplier that understands the regulations your industry must comply with. Not all filtration products comply with DWI’s Regulation 31, so it’s worth checking before committing to a purchase.
With the right supplier, finding water filtration solutions that are efficient, good value for money, and long-lasting should be easy.
