An asset is a stock, a service is a flow. Of course the cost or value of any flow can be expressed as a lump sum by means of standard arithmetical manipulations.

You may be considering the cost of providing services TO the environment, like water treatment, waste disposal or recycling. In so far as they are provided in the broad framework of a market economy, the provider can estimate the cost incurred in each case.

As for services rendered BY the environment, one can sometimes get an estimate of their value by implication, for instance by comparing the rent of a dwelling in a quiet area with a similar one in a noisy area one can get an idea of the value the market attaches to quiet.

The benefits of a health benefit to THE ECONOMY can be estimated e.g. by estimating the number of work-hours made available by freedom from ill-health due to an unhealthy environment, multiplied by a guess at the hourly value-added of the corresponding labour. Remember however that good health furthermore has benefits beyond the economy.

Quite a few environmental valuation methods exist; of course, the selection of one method over another hinges on the environmental impact to be assessed as well as data availability. The methods listed next presented in decreasing order of reliance upon market information. Market-based methods include (i) change-in-productivity, (ii) loss of earnings, and (iii) defensive or preventive expenditures. Methods based on surrogate market value have to do with (i) property value, (ii) wage differential, (iii) travel cost, and (iv) marketed goods as surrogates. Methods based on potential expenditure or willingness-to-pay include (i) replacement cost, (ii) shadow project, and (iii) contingent valuation.