When watering your polytunnel, it is always better to use rainwater that you have harvested from your roof rather than water that comes from the tap, from a mains water supply. Here are some of the compelling reasons that you should always use rainwater rather than tap water wherever possible:
Even in parts of the UK where water is not particularly in short supply, choosing to use rainwater is the sustainable choice. Rainwater is a useful, renewable resource and one that we should take full advantage of in our polytunnels and gardens. Fresh water is precious and we should take care to use it wisely. A mains supply always takes energy to maintain and is not as eco-friendly an option in most cases.
Those whose mains water supply is metered will find that the cost of using water from that supply in a polytunnel can quickly add up. To save a lot of money on household bills in that instance, it is best to use instead the free supply of water that falls from the sky. Why pay for something that falls on your land and can be collected free of charge?
Not only is rainwater a free and sustainable resource, it is also superior to most tap water supplies for the health of plants. Rainwater, unlike many mains supplies of water, will not contain chlorine, nor other chemicals that are often found in tap water. Some plants will do much better when not subjected to water adulterated with other such substances.
Rainwater is also far less likely than tap water to effect the pH of the soil in your polytunnel and garden. Rainwater generally has a neutral pH and so will not deteriorate the conditions in which your plants grow, allowing them to thrive as nature intended.
It is easy to add a rainwater harvesting system to your growing plans. Simply attach a barrel or water butt to the down pipe on your home and on any ancillary building on your land. These containers can store all the water that falls on your roof and can then be used for watering your plants throughout much of the year.