REVENUE RECOGNITION, Disaggregated Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
REVENUE RECOGNITION [Abstract]
Refund to customers through reduced tariff rates			$ (3,800)
Increase in reserve for bad debt	$ 500			$ 500
Minimum number of days due for accounts receivable from SLP Plan customer				25 days
Minimum number of days customers services invoiced in advance				30 days
Disaggregation of Revenue [Abstract]
Other Operating Revenue not in scope of ASC 606	432	$ 381		$ 1,046	$ 993
Total Operating Revenues	24,737	22,549		66,390	62,586
Tariff Revenue [Member]
Disaggregation of Revenue [Abstract]
Total Operating Revenues	22,936	20,850		61,268	57,455
Tariff Revenue [Member] | Consumption Charges [Member]
Disaggregation of Revenue [Abstract]
Total Operating Revenues	13,875	12,844		36,217	34,320
Tariff Revenue [Member] | Fixed Fees [Member]
Disaggregation of Revenue [Abstract]
Total Operating Revenues	6,797	6,529		20,192	19,525
Tariff Revenue [Member] | Service Charges [Member]
Disaggregation of Revenue [Abstract]
Total Operating Revenues	21	133		183	467
Tariff Revenue [Member] | DSIC [Member]
Disaggregation of Revenue [Abstract]
Total Operating Revenues	1,392	1,334		3,810	3,129
Tariff Revenue [Member] | Industrial Wastewater Services [Member]
Disaggregation of Revenue [Abstract]
Total Operating Revenues	851	10		866	14
Non-Tariff Revenue [Member]
Disaggregation of Revenue [Abstract]
Total Operating Revenues	1,369	1,318		4,076	4,138
Non-Tariff Revenue [Member] | Service Line Protection Plans [Member]
Disaggregation of Revenue [Abstract]
Total Operating Revenues	1,099	1,039		3,267	3,117
Non-Tariff Revenue [Member] | Contract Operations [Member]
Disaggregation of Revenue [Abstract]
Total Operating Revenues	207	210		636	866
Non-Tariff Revenue [Member] | Inspection Fees [Member]
Disaggregation of Revenue [Abstract]
Total Operating Revenues	$ 63	$ 69		$ 173	$ 155