CACTUS collects costs from existing and completed operational sanitation systems, rather than from a bottom up design basis. The approach is based on a number of key concepts which can be summarised as follows:

• CACTUS costs are based on semi-analytic estimation, and are therefore ball park estimates, commensurate with strategic or conceptual planning rather than detailed design or construction estimates.
• CACTUS costs estimates are predicated on the assumption that a single virtual service provider provides services across the entire value chain (collection, emptying, transport, treatment). While this is rarely true in practice, it means that transfers between the steps of the value chain are not included in the costs estimates, and the focus is on real costs of ‘Make’ and ‘Buy’ elements of the system (see Figure 1).
• CACTUS recognises that most service providers lack complete information on total costs incurred and/or are unable to report on all costs (for example taxes may not be paid, or the cost of land purchase may be offset). Ultimately we intend to fill all missing data gaps using averaged data from the CACTUS database but currently such gaps are usually filled in consultation with delivery partners and/or through inspection of the existing database.

CACTUS uses two standard cost metrics to describe costs associated with different sanitation service delivery options.

• Total Annualised Cost Per Household (TACH)
• Total Annualised Cost per Capita (TACC)

Total Annualised costs include capital costs annualised over the lifetime of the relevant infrastructure or equipment, including costs of capital and discounting, plus the annual operational costs associated with that element of the sanitation service delivery option.

All costs are normalised in the database to a single currency and date to allow for easy comparisons.