This question is more of a national issue than just for Hampshire/West Sussex.
There are areas in this country that have plenty of water, why can we, as a country, not transfer water from those areas that have an over supply to those that are in need.   Obviously this would need a network of pipelines and there would be opposition due to the cost.   However this is an important issue and should be looked into.
We used to live in Chard, Somerset.   Water is constantly flowing in two streams either side of the road in the town, one stream empties into the Bristol Channel abd one into the English Channel.   What a waste of a resource.  I am sure that there are other places with a surplus that could be transferred.