Demand Management series by Dr Ronnie McKenzie – Part 2 of 4: Non-revenue Water / Pressure Reduction

Part two of our interview with Dr Ronnie McKenzie on the topic of Demand Management.

If you had to generalize, what are the top four ways to reduce service area demands?

1. I would say the most cost-effective thing that you can do is to repair reported leaks as quickly as possible. Don’t allow them to continue running. Also try and repair even the small leaks, not just the large leaks. A small leak running for six months to a year is going to lose much more water than a big leak that you repair within a day or so. So, the first thing to do is repair visible leaks that have been reported. Get them out of the way.
2. The next thing to do is to search for leaks that have not been reported. You can identify the areas that you want to address by monitoring the minimum night flows. This will be a key indicator of leakages. If the minimum night flow is abnormally high, that is an indication that you have a problem. We believe that if the minimum night flow is under control, then the leakage is under control.
3. A third option is to reduce water pressures throughout the system if possible, through the use of pressure reducing valves (PRVs) since pressure drives leakage. If you can keep the average pressures and the pressure spikes under control, then you can minimize the number of new pipe bursts. You can also manage and even reduce background leakage which is the sum of all the small water leaks in a water reticulation system that are too small to find using standard leak detection equipment.  Such background leakage will always be present in a water reticulation system and if not managed properly, it can become a significant contribution to water losses.    The only way of tackling background leakage is through pressure management or by replacing the water network – which is a last resort due to the prohibitive costs involved with pipe replacement.  By adding PRVs into the system you can manage the system pressures to reduce losses and at the same time eliminate pressure spikes/transients from moving through the system.  Such pressure spikes (often called water hammer) can be very damaging to the reticulation system and create new burst pipes.
4. Metering is another area to consider. However, the original International Water Association (IWA) integrated development environment (IDE) recommendation of 2,000 connections per district metered area (DMA) is not always applicable and should be considered as a rough guideline and not a rigid rule.The problem with DMAs is that they themselves don’t reduce wastage. DMAs, when used properly, help manage the system and identify specific areas where you may have a problem.  It is basically a process of cutting a large area up into smaller areas where you can manage and identify problems more easily.   If you have enough money to cut your areas into separate small DMA’s then it can be a very effective management strategy.   The problem that is often overlooked when setting up DMAs is the fact that once a DMA has been established, it must be maintained, or it serves no purpose.  Invariably people will open or close valves that shouldn’t be opened or closed and by doing so, they inadvertently compromise the DMAs.   Unless the water utility specifically sets aside budget and resources to maintain any DMAs that it plans to establish, it will waste money on something that will last a few months before the different zones are eliminated through the unauthorised opening of boundary valves.  In simple terms, if you’re not going to manage the DMAs, then don’t bother creating them in the first place.   An alternative approach which may be better for water utilities that do not have the budget to maintain hundreds of small permanent DMAs is to adopt an approach of creating a few large DMAs and combing this with regular step-testing.    Step-testing involves carrying out a monitoring (logging) exercise during the night and closing off various portions of the network by shutting off valves and slowly reducing the size of the area that is still pressurised.  By monitoring the nightflow during this exercise, it is possible to identify which parts of the system are responsible for most of the leakage.  In my experience I have seen many instances where a water utility will spend a lot of money on the establishment of small DMAs only to have them totally compromised within six months to a year.   The more DMAs you have, the more maintenance you must spend on maintaining them and keeping them operative.

   For some, DMA’s is a contentious issue. My personal view, if DMA’s are to be used, is to set up larger zones (i.e., needing fewer number of DMAs) and just manage them properly. And, if you find the minimum night flows in the large DMA too high, then cut the DMA into smaller zones and fine tune the search for leakages. If you’ve got a large DMA, that has a low minimum night flow, then you don’t need to cut the area into any smaller DMAs as to do so you are just wasting money.

What are the areas that you would recommend that they monitor?

I would suggest monitoring both pressures and flows if possible since they both help to identify the health of a system.  I would also recommend monitoring the minimum night flow carefully and adding an alarm to the system to pick up any increases in the minimum night flow which usually suggests that new leakage has occurred.

I would also recommend monitoring:

• office parks
• the top 100 or 200 highest customers
• townhouse complexes
• shopping centres
• prisons and municipal offices
• all bulk water meters and reservoir storages

I don’t believe it’s always necessary to have every single customer monitored. You are looking for cost effectiveness. So, I do believe in the “80 /20 principle”; and, rather go for hardware/software that can last for five to 10 years rather than go for the cheapest equipment that will be broken within a year or so.