The water cylinders are the best route to go down, more economical, and they are well insulated these days. I shut mine off at night and the water is still okay to shower the next day.
There is a company called Matelfon they are based in Deltebre but they cover Tortosa also. One of the owners is called Carlos and he has good English. They cover plumbing electrics air con and heating.
I have used them several times and have found them very good value and quality.
Tel 977 482 174
www.matelfon.com
Ctra. Canal, palcel-la 41. 43580 Deltebre- La Cava
I am not on commission and have no links, but I think firms that provde a good service should be known about.
Before I knew of them I used a local electrical company to renew a mains panel and paid 400€. My neighbour had the same job done with Matelfon at half the price. That's how I learned of them.
I hope it's of some use to you.