SustainableSources.com: Water Budget

Water Budget

CONSIDERATIONS
IMPLEMENTATION ISSUES
GUIDELINES

INDOOR BUDGET
Indoor Example
OUTDOOR BUDGET
Outdoor Example

DEFINITION:

The indoor and outdoor water budgets are the calculated amount of water a household will require based on the size of the family, number and types of fixtures, and landscape needs. The landscape needs are based on turf water requirements only.

CONSIDERATIONS:

The goal of the water budget is to show the homeowner how much water is used in the house. The flow rates of the fixtures and the appliances provided by the builder (i.e. commodes, faucets, showerheads, dishwashers) and added by the homeowner (i.e. clotheswasher) can be put in a budget form that helps the homeowners understand their water use.

The primary exterior demand for water is for watering lawns. The water budget format tells the homeowner how much water their turf should require based on size and type of grass.

The water budget establishes a baseline of how much the homeowner should expect to use in the house and where the water goes. Additional conservation strategies can be designed from the water budget information.

The figures derived from the Water Budget calculations are estimates. Personal lifestyle will determine the actual water use.

	T E C H N O L O G Y	F I N A N C I N G
	Commercial Status	Implementation Issues
Indoor Water Budget
Outdoor Water Budget

	Satisfactory
	Satisfactory in most conditions
	Satisfactory in Limited Conditions
	Unsatisfactory or Difficult

IMPLEMENTATION ISSUES

FINANCING:

Not applicable

PUBLIC ACCEPTANCE:

Good, if clearly presented.

REGULATORY:

Not applicable

GUIDELINES

1.0 Indoor Budget

Based on the average per capita interior water use rates developed and used by the U.S. Housing and Urban Development (HUD).

Actual use rates for water fixtures will vary.

Some items in the indoor budget could be added to the home after the homeowners move in. Use average water amounts for fixtures that are not in place. This helps the homeowner decide whether to add a fixture or appliance that is more conserving than the average because they can see how it can affect the total.

Directions: The water-using items are listed in the left-hand column. The use rate per person per day is shown in the next column. The third column is filled in with the flow rate. For example, the rating of gallons of water used per flush and the rated flow rate on the showerhead would be entered in this column.

Multiply the second column times the third column then times the fourth column (this is the number of persons in the household). The subtotal for each item is entered in the fifth column.

The figures in the fifth column are added up to show the amount of water used each day. This total can be multiplied by 365 (days) to give the amount of water that would be consumed in one year.

Use this Worksheet to calculate your own home.

INDOOR WATER BUDGET EXAMPLE

Fixtures and appliances in this home have the following flow rates:

Toilets	1.6 gallons per flush
Showers	2.5 gallons per minute
Washing Machine	The family will buy a model using 35 gal. per load
Dishwasher	8.5 gal. per load
Faucets	This amount is fixed at 8.5 gallons
Baths	Average use

Family size: 3

ITEM	USE RATE	FLOW RATE	# OF PERSONS	TOTAL
Toilet	4.0 flushes per person per day	1.6	3	19.2
Shower	4.8 minutes per person per day	2.5	3	36
Washing Machine	0.30 loads per person per day	40 gal per load (avg.)	3	36
Dishwasher	0.17 loads per person per day	8.5	3	4.34
Faucets			N/A	8.5 estimated
Baths	0.14 baths per person per day	50 gal. per bath (avg.)	3	21
TOTAL				125.04

Daily total (125.04) times 365 days equals 45,639.6 gallons per year.

Use this Worksheet to calculate your own home.

2.0 Outdoor Water Budget

The calculation method is for sunny turf (lawn) areas only. Shaded lawn areas will have reduced water requirements. Soil type can also affect water demand. If no lawn is present and there is a maintained landscape, use water requirements provided by the nursery or landscape designer. This method will give a general indication of water demand only.

To minimize water needs for turf areas, do not remove grass clippings, keep grass at the recommended cutting height with frequent cuttings, and use a natural soil amendment such as “Dillo Dirt.” Note that watering rates will vary during the year, with most watering occurring in the summer. (See the Xeriscape Section.)

The outdoor Water Budget can be calculated for 5 (five) grass types.

OUTDOOR WATER BUDGET EXAMPLE

Grass Type Factor Chart
St. Augustine	1.0
St. Augustine/Bermuda Mix	0.9
Zoysia	0.9
Bermuda	0.8
Buffalograss	0.5

Calculation Sequence (chart follows):

Step 1:

Multiply 50 (inches of turf water demand for one year not including natural rainfall) times square feet of turf area (SQFT) divided by 12. This gives the cubic feet of water demand per year. (CF/YR)(50 x SQFT) / 12 = CF/YR

Step 2:

Multiply cubic feet of water demand per year (CF/YR) times 7.48 (a conversion factor) times the grass type factor (GTF from the above table). This gives the gallons per year (G/YR) required by the selected grass type.CF/YR x 7.48 x GTF = G/YR

Step 3:

Multiply 32 (inches of natural rainfall) times square feet of turf area (SQFT) divided by 12 gives the cubic feet of water supplied per year by rainfall (CFNR/YR).(32 x SQFT) / 12 = CFNR/YR

Step 4:

Multiply the cubic feet of natural rainfall per year (CFNR/YR) times 7.48 to get the gallons of natural rainfall (GNR).CFNR/YR x 7.48 = GNR

Step 5:

Subtract the gallons of natural rainfall (GNR) in Step 4 from the required water for the selected grass type (G/YR) in Step 2. The remainder is the amount of additional irrigation water the lawn will require. If the number is negative, that means natural rainfall is adequate to keep the grass alive although water may be added to keep it looking green during extended dry periods.G/YR – GNR = water requirement in gallons

Use this chart and Legend to fill in the Outdoor Water Budget for your own home.

Grass Type Factor Chart
St. Augustine	1.0
St. Augustine/Bermuda Mix	0.9
Zoysia	0.9
Bermuda	0.8
Buffalograss	0.5

OUTDOOR WATER BUDGET EXAMPLE

GRASS TYPE:                 BUFFALOGRASS
GRASS TYPE FACTOR (GTF):    0.5
SQUARE FEET OF TURF (SQFT): 5,000
NATURAL RAINFALL (NR):      32

SQFT: square feet of turf..................5000
CF/YR: cubic feet per year.................20,833
GTF: Grass Type Factor.....................0.5
G/YR: gallons per year.....................77,915
CFNR/YR: cubic feet of natural rainfall....13,333
GNR: gallons of natural rainfall...........99,733
NR: natural rainfall (Austin = 32).........32

STEP 1

50 X 5,000 SQFT / 12 = 20,833 CF/YR

STEP 2

20,833 CF/YR X	7.48 X	0.5 GTF = 77,915 G/YR

STEP 3

32 NR X 5000 SQFT / 12 = 13,333 CFNR/YR

STEP 4

13,333 CFNR/NR X 7.48 = 99,733 GNR

STEP 5

77,915 G/YR (Step 2) - 99,733 GNR(Step 4) = -21,818 WATERING REQUIREMENT

This means that for 5000 square feet of Buffalo grass, 32 inches of rain gives almost 22,000 gallons more than is needed.

If calculated for the other grass types, 5,000 square feet of turf will require from almost 27,000 gallons for Bermuda to over 58,000 gallons for St. Augustine.

Use this chart and Legend to fill in the Outdoor Water Budget for your own home.

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