(1) I think a reservoir is a good idea, it WILL benefit wildlife. Don't bother with Natural England, they're a quango who know bugger all about wildlife. 
(2) As regards "Community Facilities" at the reservoir development, can you make sure Fishing & other Bloodsports will be banned.
(3) You mentioned about Southern Water paying for this reservoir - are their customers going to pay higher bills, or are their shareholders & fat cat executives going to take a pay cut ? I hope you've done your sums right because Southern Water need enough funds to pay court orders for their diabolical service.
(4) Ground Water sources are in danger of being contaminated through Fracking, which the government are relentlessly pushing ahead with. So it makes sense to find alternative sources of clean water. Would the hardness of the water be the same, or will it be softer ?
(5) Your claim that Portsmouth Water is the cheapest is questionable. South West Water customers receive a rebate from the government, and because they both supply clean water & remove waste water, only 1 water bill is payable by consumers - reducing admin costs. 
(6) I've also shared this survey on Facebook so that you are able to reach a larger audience.