|Your online product catalog list 19 cultivars of Thuja occidentalis. For three of them ('Degroot's Spire', 'Filiformis' and 'Teddy'), the water requirement is stated to be 'Once established needs only occasional water'. The water requirement for the other 16 is shown as 'Water regularly, when top 3|
|Degroot's Spire is a smaller plant and so technically will require less water than the other arborvitaes. The plants you mention will grow deep roots if watered deeply while they're becoming established. Grown in the ground, Degroot's Spire will appreciate a deep soaking once each week during the hottest months of the year; grown in a container, it will need more frequent applications of water.
Hope this answers your question!