I deal with all of these things often, which people are keen on nationalising, here's my take:
Rail is in a horrendous state, but most of the problem is caused by the part which is already nationalised and has always been nationalised (Network Rail). Until NR are sorted out no rail operator stands a chance of having reasonable fares and being profitable, with reasonably paid staff and a reasonable amount of services. Ask anyone who deals with or works for NR, they will 100% agree, they're an absolute red tape inducing, cost inflating, public fleecing bandit. Another good example of how bad we are at nationalised rail is HS2, which is a public company which wastes money for fun. This is a shame as it's a 100% necessary project too, well the full version would have been anyway.
Water (well the sewerage arm) is a black hole too, infrastructure for sewerage has been bad for 20 years, and we need to split out foul and surface water sewers from being combined systems, to cuit down on pollution etc. This would be tough, starting from scratch out in the open, but doing this in towns and cities where every drain has gas, water, electric, telecom, fibre, mobile cables, cars, trains, crap roads and infrastructure over the top of it makes it a massive can of worms. This is why the water companies have been kicking the can down the road not trying to sort it out, whilst funnelling profits out the back door. The second they switch to nationalised, to sort out the issues over the next 50 years, there won't be any profits to pay out dividends, and would still be bankrupt if they charged double the bills. Water/ sewer charges are far to cheap too mind. There's ~100 years worth of old infrastructure which needs repairing or replacing, but also the problem is the capacity of trunk routes needs to be much more as we've got ~70m people, rather than ~40m, and the storms and SW are far worse. Effectively we need to upgrade capacity by ~50% at least, but if there is no room for additional capacity then the engineering becomes extremely complex and costly.
The actual water pipes are getting really old now too, but these are easier to replace than sewers.
Energy, best idea by a mile, generate our own, with onshore wind, and undercut the offshore wind we're already good at. This offshore wind already undercuts gas, so will get shot of that reliance on the middle east also. This is quite easy to do as it generally just means long cable routes through countryside's, which is extremely easy compared to most works. There's a ton of expertise in this sector UK based, could probably just buy out a couple of big contractors and a chain of sub contractors, and use that as a base, rather than starting from scratch. We're also good at Solar and BESS sites too, so no reason why we can't do this. Avoid nuclear, we're crap at it (largely due to our own red tape), and it's extremely expensive.