Rockland County Water Use
Different ways of measuring the amount of water used serve different purposes. The highest daily use in a year, or peak demand, is important in understanding requirements for fire protection and increased seasonal demand. It's only necessary to meet peak demand for a short period of time, however, and average demand, measured in millions of gallons/day (mgd) is used to assess the adequacy of a water provider's sustainable water supply. In assessing the potential role of increased water conservation in long-term water supply plan it's useful to look at per capita usage. We take all three perspectives below.
| Annual Average Demand (MGD) mgd = million gallons per day |
|
|---|---|
| 1970 | 19.7 |
| 1971 | 19.9 |
| 1972 | 20.8 |
| 1973 | 21.8 |
| 1974 | 22.5 |
| 1975 | 23.2 |
| 1976 | 24.2 |
| 1977 | 25.6 |
| 1978 | 25.2 |
| 1979 | 25.3 |
| 1980 | 25.9 |
| 1981 | 22.4 |
| 1982 | 23.1 |
| 1983 | 25.4 |
| 1984 | 26.1 |
| 1985 | 24.3 |
| 1986 | 24.6 |
| 1987 | 26.6 |
| 1988 | 27.7 |
| 1989 | 26.7 |
| 1990 | 27.4 |
| 1991 | 29.9 |
| 1992 | 28.3 |
| 1993 | 28.8 |
| 1994 | 28.6 |
| 1995 | 28.4 |
| 1996 | 28.0 |
| 1997 | 27.5 |
| 1998 | 28.9 |
| 1999 | 28.8 |
| 2000 | 28.6 |
| 2001 | 29.7 |
| 2002 | 26.7 |
| 2003 | 28.5 |
| 2004 | 29.2 |
| 2005 | 31.7 |
| Maximum Day Demand (MGD) mgd = million gallons per day |
|
|---|---|
| 1970 | 29.8 |
| 1971 | 33.0 |
| 1972 | 28.6 |
| 1973 | 36.2 |
| 1974 | 37.9 |
| 1975 | 35.7 |
| 1976 | 33.4 |
| 1977 | 43.0 |
| 1978 | 37.5 |
| 1979 | 37.1 |
| 1980 | 40.8 |
| 1981 | 30.7 |
| 1982 | 31.4 |
| 1983 | 37.0 |
| 1984 | 37.3 |
| 1985 | 27.7 |
| 1986 | 34.4 |
| 1987 | 38.9 |
| 1988 | 41.6 |
| 1989 | 33.1 |
| 1990 | 34.2 |
| 1991 | 44.9 |
| 1992 | 35.7 |
| 1993 | 40.7 |
| 1994 | 38.6 |
| 1995 | 40.0 |
| 1996 | 36.8 |
| 1997 | 39.2 |
| 1998 | 42.9 |
| 1999 | 44.6 |
| 2000 | 39.1 |
| 2001 | 46.5 |
| 2002 | 32.1 |
| 2003 | 37.4 |
| 2004 | 40.3 |
| 2005 | 43.5 |
Minor typos in original testimony corrected here.
| KEY |
| Drought. Not included in max demand analysis because max demand artificially reduced. Not representative. |
| Drought. However, included in analysis since water use restrictions were declared in Sept, well after max-day demand occurred. |
Historical Average Demand in Rockland County
United Water data from 1970-2005 show a general increase in average demand from the low of 19.7mgd in 1970 to the high of 31.7mgd in 2005. To put this in perspective, Rockland County sustainable water supply was assessed by UWNY to be 32-34 mgd in 2006, barely above annual demand in 2005.
Historical Peak Demand in Rockland County
United Water data from 1970-2005 show a general increase from 29.8mgd in 1970 to 43.5mgd in 2005. The low was 27.7mgd in 1985 and the highest daily demand in the period was 46.5mgd in 2001. To put this in perspective, Rockland County peak day capacity is from 44.5 - 47.5mgd. In other words, Rockland County peak demand in the summer is approaching peak day capacity. Peak day capacity is defined as the maximum amount of water that can be delivered in a day, given the currently developed resources (wells and surface waters).
In looking at the historical peak demand it's helpful to know that requests for voluntary conservation were made in 1981, 1982 and 1985 before mandatory drought restrictions were enacted as part of the Rockland Sanitary Code, and mandatory water restrictions were invoked in 1995, 1999 and 2002.
Rockland County Seasonal Water Usage
Looking at twenty years of daily system usage data on a per capita basis provides us with a way of assessing conservation potential in the future. In the table to the right, "Summer" is an average of daily per capita usage from May through August, the months during which United Water of New York charges a premium. "Winter Spring Fall" is an average of daily per capita usage for January through April and September through December. Compared to the study locations in the Residential Water Usage Study cited below, Rockland County's average increased summer usage is relatively low at 14 gallons per capita per day (gpcd). In contrast, Rockland County's average non-summer usage is relatively higher at 81, compared to a national indoor usage average of 70 gpcd. This suggests indoor water conservation measures could be an important component in Rockland County's water supply planning going forward. In order to meet peak demand requirements however the peak daily demand in relationship to average daily demand is critical, and that ratio in Rockland County is approximately 1.6.
| Year | Indoor adjusted gpcd | Summer adjusted gpcd | Outdoor adjusted gpcd |
|---|---|---|---|
| 1986 | 75 | 88 | 13 |
| 1987 | 81 | 95 | 14 |
| 1988 | 83 | 101 | 18 |
| 1989 | 83 | 90 | 6 |
| 1990 | 85 | 93 | 9 |
| 1991 | 89 | 107 | 18 |
| 1992 | 86 | 95 | 9 |
| 1993 | 83 | 103 | 21 |
| 1994 | 84 | 97 | 13 |
| 1995 | 80 | 101 | 20 |
| 1996 | 81 | 94 | 12 |
| 1997 | 78 | 94 | 16 |
| 1998 | 81 | 99 | 18 |
| 1999 | 79 | 99 | 20 |
| 2000 | 81 | 92 | 11 |
| 2001 | 81 | 100 | 19 |
| 2002 | 76 | 83 | 8 |
| 2003 | 80 | 89 | 9 |
| 2004 | 81 | 92 | 12 |
| 2005 | 83 | 101 | 18 |
| Average | 81 | 96 | 14 |
These water usage calculations are based on total water system usage through United Water, 1996-2005. The data are adjusted by subtracting unbilled water going to leaks and fire departments and by removing estimated non-residential usage
Future Water Use
In order to determine requirements for future water supply both the Rockland County Bureau of Water Supply and United Water of New York estimate what demand for water will be in the future. They look at both peak day demand (the highest water use day of the year) and average water use (average daily use for a year).
Peak Demand
Rockland County's approach to projecting future demand was to start first with a straight line regression, predicting essentially that water use in the county will continue to increase in the future at the same rate that it has increased in the past. When making this estimate Rockland County removed the years when demand was lower than normal due to mandatory conservation restrictions during declared droughts. In this way they estimate the future growth of unconstrained demand, resulting in the following peak day demand projections:
2010 - 43.5MGD
2015 - 44.7MGD
2020 - 45.9MGD
It turns out however that because of the considerable year-to-year variability the actual maximum day demand was greater than predicted by linear regression 50% of the time. Between 1970 and 2005. As a result, when Rockland County projects future demand for water it identifies a range so that it can estimate a maximum day demand number that will be as high or higher than the actual number 80, 90, or 99% of the time.
UWNY uses a different methodology to estimate future water usage with numbers that are generally higher than the Rockland County projections but generally within the 99% confidence interval. UWNY projections show an increased rate of increase in water usage out to 2020, in contrast to the Rockland County projections that predict a stable rate of increase. In his testimony to the Public Service Commission the Rockland County hydrologist speculated that the projected increased rate of increase is "likely due to the style of development recently experienced in Rockland, i.e., large single-family homes with extensive landscaping and irrigation systems." (Miller, 2006)
Average Demand
For average demand Rockland County and UWNY take the same approaches they did with peak demand with two differences:
1. Rockland County began its regression to estimate future average demand in 1981 rather than 1970 because water conserving plumbing fixtures were introduced in 1980 and the rate of increase in average water use significantly slowed.
2. UWNY's average demand projections are lower than Rockland County's 80% confidence level, suggesting that 10% of the time actual demand will be exceeded.
New York State Laws and Regulations
NYS Regulations 3.1.1 Recommended Standards for Water Works, 2003 Edition, incorporated by reference in 10 NYCRR, Part 5, Subpart 5-1.222 require that.
1. For a surface water supply the quantity of water at the source shall be adequate to meet the maximum projected water demand of the service area as shown by calculations based on a one in fifty year drought or the extreme drought of record and should include considerations of multiple year droughts and provide a reasonable surplus for anticipated growth.
2. Total developed groundwater source capacity, unless otherwise specified by the reviewing authority shall equal or exceed maximum day demand with the largest producing well out of service.
The net impact of these regulations, as interpreted by the Bureau of Water Supply, is that demand projections necessarily represent unconstrained demand, that is, water use is projected to remain at the same levels whether or not there are droughts. While these approaches are used in Rockland County, alternate approaches are used elsewhere (see box below) and could, in theory, be assessed for use here.
Another way to look at setting water supply objectives:
The objective of the water supply plan in San Francisco County, the San Francisco peninsula, and the southern East Bay is to fully meet 2030 purchase requests during non-drought years and provide sufficient water such that water supply would be reduced by a maximum of 20% during any one year of drought ( Cooley, 2007).
