How long is a piece of string ? hahaha! there are so many different varieties of succulent plants that this is an impossible question to answer in one paragraph 😀
The Desert cacti and most of the summer growing succulents do not need to be watered during the Winter months as long as they are kept cool and dry, however the Melocacti and the Epiphytes I still keep very lightly moist. Some of the Autumn and Winter growing Succulents such as some of the Mesembs, e.g Lithops and Conophytums, as well as some of the Crassulas, Tylecodons, and Aloes etc, I still keep these very lightly watered every 3-4 weeks. The Epiphytic cacti such as Rhipsalis and Schlumbergera ( Christmas and Thanksgiving cactus ) are in their flowering periods during the Autumn and Winter and should never be allowed to totally dry out like the Desert types, while no serious harm will come to them if they are kept dry for short periods over the Winter, they do have a tendency for their stems to shrivel and for many of the Schlumbergera cacti to drop their buds and blooms if the soil inside of their pots is kept too dry.
All of the Epiphytic cacti such as Schlumbergera, Rhipsalis, Epiphyllum etc come from a natural habitat of tropical and humid rainforests and grow naturally hanging from trees for support alongside other moisture loving plants like Orchids and Ferns and do not appreciate being kept dry for too long.
With all the Desert Cacti and Succulents I water them from Spring until early Autumn which in Ireland for me its March until early October. I water them only when the pots have completely dried out before watering them again. I always use overhead watering as much as possible as this helps to keep them clean and dust free and prevents Red Spider mite attack. However I avoid overhead watering with any of the ‘hairy’ ones and the Echeverias as water can sometimes collect in the hairs and rosettes and may encourage rot, so water these at the top of the pot. Overhanging plants that are hanging over their pots I water from below and place the water in the saucer, sometimes 3 or 4 waterings are given in the saucer over a series of hours until the plant has fully soaked up the water well, but I never allow water in sit in the saucer permanently as this will encourage root rot, and water still sitting in the pots after a few hours gets emptied away.
Avoid watering during the daytime on very hot and sunny days as the water droplets on the plants can act as magnifying lens behind glass and can leave scorch marks on the stems, It is better to water either first thing in the morning or last thing of an an evening.
Never water your plants with icy cold water as this will shock them and their roots, I always recommend using tepid rainwater.
Here is a video below I have made for my You Tube channel on How to water your cacti and Succulent plants :
This video goes into a lot more detail on the correct way to water your cacti and succulents.
pH of your tap water :
I always recommend using clean rainwater as much as possible to water your plants as tap water contains chemicals and often most tap water is hard water with a high pH that over time can make the pH of your soil too high which may encourage root loss and or rot. Since switching to using rainwater a few years ago my plants have thrived and I notice such a huge difference in how healthy the root systems are when I come to re-pot them, compared to years ago when I used to water them with tap water. However if you live in an area where the pH of your tap water is not hard and no higher than a pH of 7 then your tap water should be safe to use, and letting the water sit for a day or two before using can help to eliminate some of the chlorine too.
Here is a video below that I have made for my You tube channel on how to test the pH of your tap water :
You can get pH tester kits online on amazon and or ebay, these are easy to use and will tell you if your water is hard water or soft water.