When the measured radon concentration values were compared with the allowed MCL for radon concentration in water (which is 11 Bq l21) proposed by USEPA(5), it was observed that 89 % of the samples had radon concentration below this recommended value. Only in 11 % of the samples from the Sikar district the recorded values were found to be higher than the recommended value and only in 5 % of the samples, the recorded values were found to be higher than the value of radon concentration in water for human consumption (4–40 Bq l21) suggested by the UNSCEAR(2).