Watering plants on Chol Hamoed:
It is permitted to water plants on Chol Hamoed for purposes of damage prevention, such as to prevent the plants from withering if they were to not be watered. It is, however, forbidden to water plants if there will be no loss or damage involved with the plant if one were to refrain from watering it during Chol Hamoed. [Accordingly, each plant product that one has in his home, or garden, is to be individually assessed as to whether a lack of watering it during Chol Hamoed will cause it to wither, and only then is it allowed to be done. This applies whether to flowerpots, vegetable gardens, or fruit trees. Accordingly, if it suffices for the plant to be watered only once a week then it should be done prior to the start of the holiday and it will hence not be necessary to water it during the holiday.]
It is permitted to water plants on Chol Hamoed for the purpose of loss prevention, such as to prevent it from dying or withering.
May one spill water over grass or over a plant on Chol Hamoed, such as when washing hands or emptying his cup?
It is permitted for one to spill water over grass or over plants on Chol Hamoed if he is no intent to water the plant by doing so, such as while washing hands. Nevertheless, some Poskim are stringent not to spill water over plants during Chol Hamoed, even in the process of washing hands.
 Michaber 537:1 “It is permitted on Chol Hamoed to perform Melacha in order to prevent loss, therefore a field in need of irrigation may be irrigated during the Moed, as otherwise it will cause loss to the field. However, a Sedei Habaal [which is watered by rainfall] may not be watered on Chol Hamoed, as it is only watered for purposes of fattening the produce not for loss prevention.”; Tur 537; Mishneh Moed Katan 2a “Mashkin Beis Hashlachin Bamoed”; Kitzur SHU”A 104:8; See Moed Katan 6b and Rishonim there; Shut Hamabit 2:64; Kaf Hachaim 537:13; Chazon Ish 134:14; Beir Moshe 7:107; Chol Hamoed Kehilchaso 11:9; Piskeiy Teshuvos 537:3; Shemiras Hamoed Kehilchaso 7
 See Beir Moshe ibid; Chol Hamoed Kehilchaso ibid
 Beir Moshe ibid; Piskeiy Teshuvos ibid
 Michaber 537:8 regarding making a water pond in order to catch fish; Shemiras Hamoed Kehilchaso 7:9
 Orchos Rabbeinu 2:121 that so was the custom of the Chazon Ish; See SSH”K 66 footnote 181