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fermer ce livreA Guide to the Development of on-site Sanitation (WHO; 1992; 246 pages)
Afficher le documentPreface
ouvrir ce répertoire et afficher son contenuPart I. Foundations of sanitary practice
ouvrir ce répertoire et afficher son contenuPart II. Detailed design, construction, operation and maintenance
fermer ce répertoirePart III. Planning and development of on-site sanitation projects
ouvrir ce répertoire et afficher son contenuChapter 9. Planning
fermer ce répertoireChapter 10. Institutional, economic and financial factors
Afficher le documentInstitutional responsibilities
Afficher le documentHuman resources development
Afficher le documentEconomic factors
Afficher le documentFinancial factors
Afficher le documentExamples
ouvrir ce répertoire et afficher son contenuChapter 11. Development
Afficher le documentReferences
Afficher le documentSelected further reading
Afficher le documentGlossary of terms used in this book
Afficher le documentAnnex 1. Reuse of excreta
Afficher le documentAnnex 2. Sullage
Afficher le documentAnnex 3. Reviewers
Afficher le documentSelected WHO publications of related interest
Afficher le documentBack Cover
 

Examples

Example 10.1. Least-cost analysis

Two alternative on-site sanitation systems (A and B) are to be considered. The discount rate is taken to be 10%, the shadow exchange factor (SEF) for imported goods is 1.3, the shadow wage rate (SWR) for labour is 0.6, and the institutional and promotional costs are 30% of the initial capital cost. All costs are in dollars.

System A costs $ 71.80 at the initial construction stage and $ 10 for the use of a vacuum tanker every 5 years. The anticipated life of the system is 20 years. Note: the effects of inflation may be ignored.

   

Materials

Labour

   

Cost

SEF

Shadow cost

Cost

SWR

Shadow cost

Costs of pit:

excavation

     

5.00

0.6

3.00

 

lining

- bricks

15.50

 

15.50

     
   

- cement

5.00

1.3

6.50

     
 

construction

     

2.00

0.6

1.20

Costs of slab:

cement

10.00

1.3

13.00

     
 

steel reinforcing bar

3.00

1.3

3.90

     
 

aggregate

0.50

 

0.50

     
 

construction

     

2.00

0.6

1.20

   

34.00

 

39.40

9.00

 

5.40

Total economic cost

44.80

Cost of superstructure (calculated in a similar manner)

27.00

Subtotal

71.80

Cost of institutional support and sanitation promotion (at 30%)

21.50

Total economic investment cost

93.30

System B costs $ 55 for pit, slab and superstructure at the initial stage, with the same amount for a new pit and superstructure after 10 years, at the end of the original design life.

Total economic cost

55.00

Total economic investment cost

71.50

(calculated in a similar manner to System A above)

 

Least-cost analysis

System A

   

System B

Costs
(a)

Discounted costs
(a) × DF

Year

Discount factor
DF

Costs
(b)

Discounted costs
(b) × DF

93.30

84.80

1

0.909

71.50

65.00

10.00

6.20

5

0.621

   

10.00

3.90

10

0.386

55.00

21.20

10.00

2.40

15

0.239

   

123.30

97.30
(present value)

   

126.50

86.20
(present value)

By least-cost analysis, the present value of system B is slightly less than the present value of system A. However, the difference is not enough to allow one system to be chosen in preference to the other on economic grounds alone.

Example 10.2. Total annual cost per household

The total annual cost per household (TACH) is determined by multiplying the present value of each system by the capital recovery factor (CRF). Using the formula given in the text, and at an interest rate of 10% over 20 years, CRF = 0.118.

From the figures calculated in Example 10.1:

System A

System B

Present value = $ 97.30

Present value = $ 86.20

TACH

= 97.30 × 0.118

TACH

= 86.20 × 0.118

 

= $ 11.50 per household per year

 

= $ 10.20 per household per year

Example 10.3. Financial and affordability analysis

Using the figures given in Example 10.1 for system A, it is assumed that the householder is contributing time to excavate the pit and to construct the slab and superstructure.

 

Financial costs to be paid by household

 

$

 

Labour

0.00

(given by household)

Bricks

15.50

 

Cement

5.00

 
 

10.00

 

Steel

3.00

 

Aggregate

0.00

(collected by household)

Total

33.50

 

Superstructure

14.50

(assumes household labour contribution of 12.50)

Total

48.00

 

Determination of repayments

Assuming a subsidized interest rate of 5% with the loan to be paid off over two years:

Capital recovery factor

= 0.538

Annual loan repayments

= 0.538 × $ 48.00

 

= $ 25.80

Check on affordability: annual average household income estimated for this example as $ 380.

This would normally be too high for a household to pay, so repayments over four years at a subsidized rate of interest of 3% should be considered:

Capital recovery factor

= 0.270

Annual repayments

= 0.270 × $ 48.00

 

= $ 13.00

This may be acceptable, depending upon the cost of living, and repayments would be completed before the first pit-emptying cost is incurred. As an alternative to subsidizing the rate of interest, it might be possible to sell the latrine slab at a reduced cost. It would be unwise to sell the cement or steel at reduced cost because of the dangers of the materials being used for other purposes. Another alternative is to encourage the use of different building materials to reduce the cost of the superstructure.

Affordability with loan at full rate of interest, repayable over 4 years, slab sold at half price and reduced cost superstructure:

 

Financial costs to be paid by household

 

$

 

Labour

0.00

 

Bricks

15.50

 

Cement

5.00

 

Cement

as half price slab

6.50

 

Steel

     

Aggregate

0.00

 

Total

27.00

 

Superstructure

9.50

(reduced-cost design)

Total

36.50

 

Capital recovery factor

= 0.315

Annual loan repayments

= 0.315 × $ 36.50

 

= $ 11.50

Determination of subsidy

With subsidized rate of interest: assuming a real interest rate of 10%, capital recovery factor = 0.315 for four years. Without subsidy, annual repayments would be $ 15.10. With a subsidized rate of interest of 3%, subsidy = $2.10 annually for four years in addition to the institutional and promotional costs paid by the agency of approximately $ 22.

With subsidized slab cost: the subsidy represents half the cost of a householder making a slab. Therefore the agency has to pay labour charges as well as half the material costs. Subsidy = $ 2.00, labour and materials = $ 6.50, total subsidy = $ 8.50, in addition to the institutional and promotional costs.

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