Moed Katan, Chapter One, Mishnah One
The first mishnah of Moed Katan deals with watering a field during the festival. Watering a field is sometimes necessary or the crops will be lost. Therefore, watering in these types of situations tends to be permitted. However, watering is also quite laborious and hence some types of watering are prohibited.
1) They may water an irrigated field during the festival [week] or in the sabbatical year, both from a newly-emerging spring and from a spring that is not just emerged.
2) But they may not water the field with water from stored rain, and not with a swipe and bucket.
3) And they may not make small ditches around the vines.
Section one: An irrigated field refers to a field that cannot subsist on rainwater alone. Therefore, the mishnah allows one to water it on the festival.
During the sabbatical year it is forbidden to work the land. However, irrigating a field is not considered to be working the field, as is plowing or planting. Nevertheless, the rabbis did prohibit watering during the sabbatical year, but they did not prohibit watering a field that needed to be irrigated.
Certainly the field may be watered through an old spring, whose water has already been directed at the field. The mishnah says that it may be watered even from a new spring, despite the extra work of directing the water to the field.
Section two: Carrying water to the field from a cistern of stored rain water is a lot of work. Therefore they are not allowed to water the field in this way. They are also not allowed to water using a method called swipe and bucket, which was a type of sweeping pump used to get water out of deep cisterns. This was also considered too laborious. We can see that first the mishnah allows watering these types of fields because otherwise the crops will be lost. It then limits that by saying that some labors are prohibited because one shouldnt be doing so much work on the festival.
Section three: Finally, one may not make water ditches around vines. These ditches were made so that they would fill up and the water would seep into the roots. Again, digging these ditches was considered too much work for it to be permitted on the festival.