DRINKING WATER in the Washington area is probably as good as or better than average as far as organic chemicals are concerned. But comparisons are hard to make because the quantities involved are so small as to be often unmeasurable and, in any case, vary widely from season to season.

Drinking water in the District of Columbia is the responsibility of the Army Corps of Engineers and has been since the Civil War. According to Harry Ways, chief of the Washington Aqueduct Division, chloroform has been measured regularly only for the last three months, the highest level encountered being 81 per billion.

Chemists at the Naval Research Laboratory detected even smaller quantities of some 32 organic chemicals in D.C. drinking water during a spot check in 1974. Ways does not have the equipment to check these results.

Montgomery and Prince George counties receive water from the Washington Suburban Sanitary Commission. Tests conducted earlier this year showed an average level of 20 parts per billion of chloroform. A reading of 500 parts per billion was registered last June. The Fairfax County water system is being monitered by the EPA, which, over a recent six-month period, detected an average level of 150 parts per billion of chloroform and a maximum of 310.

The health significance of these particular levels cannot yet be assessed. It mau be nil or, at worst, present a possible threat for lifetime exposure. The standard of 100 parts per billion for all trihalomethanes (of which chloroform is the major component) is being considered by the EPA as much on the basis of what can feasibly be attained as for any particular health considerations.

For those who wish to drink water without chloroform, one solution is to buy bottled spring water. Another is to boil the water, which removes chloroform and other volatile chemicals. A third method is to install one of many home filtration devices now on the market.

But, according to Robert Harris of the Environmental Defense Fund, none of these devices is of proven efficacy and with some there is the risk of bacterial growth if the filters are not replace often enough. The answer, perhaps, is to dig a well or not to worry.