The books say you can use rainwater that's under 100 TDS without fear of problems
with your plants, mine comes off the greenhouse and garage roof and its 20-30 TDS
in different parts of the country their tap water is under 100 TDS and can be used
sadley my tap water is around 350 TDS so totally useless, as with many members
last summer was a complete washout no rain for weeks so I also bought a RO system
for a backup, so nothing to fear this summer, happy growing come on spring.