New Jersey’s three transportation Metropolitan Planning Organizations (1) project an 18 percent increase in population from 2010 to 2040, to roughly 10.4 million. Our current population is 9 million. What will the increased population do to our public water demands?
The answers require looking at a lot of moving parts. I recently published a report for the New Jersey Department of Environmental Protection (NJDEP) on water demands in the year 2040. (2) The NJDEP commissioned this report in 2014 to support future improvements to the New Jersey Statewide Water Supply Plan.
For each of the state’s 584 public community water-supply (PCWS) systems, we assessed many scenarios for how existing demands could change in response to population changes and water conservation and efficiencies at all levels. As with all models, the answers depend heavily on the assumptions used.
The final results? Depending on whether or not we are aggressive about water conservation by utilities and customers, New Jersey’s PCWS systems may, in aggregate, need somewhat more water in 2040, but could need significantly less. In other words, we have the ability to conserve our way to an even better water-supply situation than exists today, despite having 1.4 million more people. Achieving that result will take significant effort and money, especially to reduce system water losses due to aging pipelines.
Roughly nine out of 10 residents in New Jersey get their drinking water from PCWS systems. These systems can be small, such as a mobile home park or apartment complex serving a few score residents. Of the largest systems, a few serve more than a half-million residents. It may be surprising to many that only 13 systems serve half of all residential customers, and only 37 systems serve 80 percent. The other 20 percent of residential customers are served by 547 systems!
Net Immigrant Migration
Population forecasts rely heavily on trends that can change. It isn’t uncertainties in birth and mortality rates that make the big difference, though. The real complication is net migration. New Jersey’s net domestic migration rate has been negative for decades. More people leave to other states than come from other states. However, our net migration rate includes foreign immigration, and that has helped New Jersey grow. The problem is the foreign immigration rates change far faster and far more than other population trends and are sensitive to both the economy and federal policy. If anyone knows what our policies and economy will be over the next 23 years, I want to borrow your crystal ball! As a result, water demand projections need to be reanalyzed periodically to catch up with changing trends.
Water demands for public systems include many components, such as residential, industrial, commercial, and public institution water uses, plus water losses. The NJDEP has been tracking total demands for PCWS systems since 1990. Despite the addition of more than 1 million people from 1990 to 2010 (15 percent), total public demand has not increased. One reason is better water-using appliances and fixtures such as dishwashers, clothes washers, sink faucets, and showerheads. The other is the loss of water-using industry. Unfortunately, we don’t know how much of the per capita demand reduction is related to each cause. As a result, we needed to better understand one major component of demand: residential uses.
Some of the state’s largest PCWS systems provided multiyear, monthly data on residential demands for the project, representing a total population of 3.6 million. We used this data to understand how residential demands differ, per person, among high-, medium-, and low-density residential development in the various regions of the state. One key result is that low-density development has double the demand of medium- and high-density development, especially in coastal counties, which emphasizes the importance of zoning for our water future. Urban development makes water supplies stretch a lot farther.
North versus South
We were able to assess system water losses also; these are due to leaks in utility pipelines but also in customer service lines (on private property between the street and the water meter within the building). While the water-loss information is a bit fuzzy, it provides a good start in assessing statewide losses. Perhaps the most important finding is that on average, systems in northern New Jersey, which are in bedrock geology, have water losses much higher than similar systems in the coastal geology of southern New Jersey, roughly triple. That makes sense, as the coastal systems don’t have the high water pressure needed to push water up hills, and they are newer on average.
Using the demand and water loss information, population projections, and various assumptions regarding demand trends and system water losses, we provided demand projections for 14 scenarios. Let’s focus on the scenario with the best results for New Jersey. If we assume that per-person residential demands will continue to decline gradually, and that utilities all implement fairly aggressive water-loss reduction programs, the largest 37 systems (with 80 percent of all customers) could need over 10 percent less water than now, despite receiving nearly all the population growth. What is true of the group is not true for all. Of those 37 systems, 11 would need at least somewhat more water. However, only one of the largest 10 systems would need more water, Jersey City MUA.
What would it take to get to this beneficial result, and can we do even better? At a minimum, it requires continued population growth in the more densely-developed areas, gradual improvements in residential water-use efficiencies, and aggressive water-loss controls. We can indeed do better. More aggressive residential conservation can provide real benefits, especially regarding lawn sprinkler systems that currently waste water. While the results are useful for planning purposes, they shouldn’t be seen as sure predictors of the future. For these reasons, the NJDEP will need to test these results as new data becomes available.
The conclusion we draw is that growth need not increase statewide demands. Where demands would increase for specific systems, we need to make sure that demands will not exceed supplies. On the other hand, if we shift back to a lot of low-density growth and continue to have high water losses, the situation could be very harmful to our water-supply sustainability.
1. North Jersey Transportation Planning Authority, Delaware Valley Regional Planning Commission, South Jersey Transportation Planning Organization