diff --git a/core/src/Ribasim.jl b/core/src/Ribasim.jl
index d98d5a609..ca675a366 100644
--- a/core/src/Ribasim.jl
+++ b/core/src/Ribasim.jl
@@ -44,7 +44,9 @@ using Graphs:
     inneighbors,
     nv,
     outneighbors,
-    rem_edge!
+    rem_edge!,
+    induced_subgraph,
+    is_connected
 
 using Legolas: Legolas, @schema, @version, validate, SchemaVersion, declared
 using Logging: with_logger, LogLevel, AbstractLogger
diff --git a/core/src/create.jl b/core/src/create.jl
index 46a5f9ada..66e331e06 100644
--- a/core/src/create.jl
+++ b/core/src/create.jl
@@ -199,6 +199,12 @@ const nonconservative_nodetypes =
 function generate_allocation_models!(p::Parameters, config::Config)::Nothing
     (; graph, allocation_models) = p
 
+    errors = non_positive_allocation_network_id(graph)
+
+    if errors
+        error("Allocation network initialization failed.")
+    end
+
     for allocation_network_id in keys(graph[].node_ids)
         push!(
             allocation_models,
diff --git a/core/src/solve.jl b/core/src/solve.jl
index f93a76ad5..2087f2f35 100644
--- a/core/src/solve.jl
+++ b/core/src/solve.jl
@@ -415,6 +415,32 @@ struct User <: AbstractParameterNode
         allocated::Vector{Float64},
         abstracted::Vector{Float64},
     }
+
+    function User(
+        node_id,
+        active,
+        demand,
+        allocated,
+        return_factor,
+        min_level,
+        priorities,
+        record,
+    )
+        if valid_demand(node_id, demand, priorities)
+            return new(
+                node_id,
+                active,
+                demand,
+                allocated,
+                return_factor,
+                min_level,
+                priorities,
+                record,
+            )
+        else
+            error("Invalid demand")
+        end
+    end
 end
 
 "Subgrid linearly interpolates basin levels."
diff --git a/core/src/utils.jl b/core/src/utils.jl
index daeb1ca00..7d2bd8e64 100644
--- a/core/src/utils.jl
+++ b/core/src/utils.jl
@@ -101,6 +101,10 @@ function create_graph(db::DB, config::Config, chunk_sizes::Vector{Int})::MetaGra
         end
     end
 
+    if incomplete_subnetwork(graph, node_ids)
+        error("Incomplete connectivity in subnetwork")
+    end
+
     flow = zeros(flow_counter)
     flow_vertical = zeros(flow_vertical_counter)
     if config.solver.autodiff
diff --git a/core/src/validation.jl b/core/src/validation.jl
index 8ff6e59cc..f74d03eb8 100644
--- a/core/src/validation.jl
+++ b/core/src/validation.jl
@@ -636,3 +636,46 @@ function valid_subgrid(
 
     return !errors
 end
+
+function valid_demand(
+    node_id::Vector{NodeID},
+    demand::Vector{
+        Vector{LinearInterpolation{Vector{Float64}, Vector{Float64}, true, Float64}},
+    },
+    priorities::Vector{Int},
+)::Bool
+    errors = false
+
+    for (col, id) in zip(demand, node_id)
+        for (demand_p_itp, p_itp) in zip(col, priorities)
+            if any(demand_p_itp.u .< 0.0)
+                @error "Demand of user node $id with priority $p_itp should be non-negative"
+                errors = true
+            end
+        end
+    end
+    return !errors
+end
+
+function incomplete_subnetwork(graph::MetaGraph, node_ids::Dict{Int, Set{NodeID}})::Bool
+    errors = false
+    for (allocation_network_id, subnetwork_node_ids) in node_ids
+        subnetwork, _ = induced_subgraph(graph, code_for.(Ref(graph), subnetwork_node_ids))
+        if !is_connected(subnetwork)
+            @error "All nodes in subnetwork $allocation_network_id should be connected"
+            errors = true
+        end
+    end
+    return errors
+end
+
+function non_positive_allocation_network_id(graph::MetaGraph)::Bool
+    errors = false
+    for allocation_network_id in keys(graph[].node_ids)
+        if (allocation_network_id <= 0)
+            @error "Allocation network id $allocation_network_id needs to be a positive integer."
+            errors = true
+        end
+    end
+    return errors
+end
diff --git a/core/test/create_test.jl b/core/test/create_test.jl
new file mode 100644
index 000000000..946d6664f
--- /dev/null
+++ b/core/test/create_test.jl
@@ -0,0 +1,89 @@
+@testitem "Non-positive allocation network ID" begin
+    using MetaGraphsNext
+    using Graphs
+    using Logging
+    using Ribasim
+    using Accessors: @set
+
+    graph = MetaGraph(
+        DiGraph();
+        label_type = Ribasim.NodeID,
+        vertex_data_type = Ribasim.NodeMetadata,
+        edge_data_type = Symbol,
+        graph_data = Tuple,
+    )
+
+    graph[Ribasim.NodeID(1)] = Ribasim.NodeMetadata(Symbol(:delft), 1)
+    graph[Ribasim.NodeID(2)] = Ribasim.NodeMetadata(Symbol(:denhaag), -1)
+
+    graph[1, 2] = :yes
+
+    node_ids = Dict{Int, Set{Ribasim.NodeID}}()
+    node_ids[0] = Set{Ribasim.NodeID}()
+    node_ids[-1] = Set{Ribasim.NodeID}()
+    push!(node_ids[0], Ribasim.NodeID(1))
+    push!(node_ids[-1], Ribasim.NodeID(2))
+
+    graph_data = (; node_ids,)
+    graph = @set graph.graph_data = graph_data
+
+    logger = TestLogger()
+    with_logger(logger) do
+        Ribasim.non_positive_allocation_network_id(graph)
+    end
+
+    @test length(logger.logs) == 2
+    @test logger.logs[1].level == Error
+    @test logger.logs[1].message ==
+          "Allocation network id 0 needs to be a positive integer."
+    @test logger.logs[2].level == Error
+    @test logger.logs[2].message ==
+          "Allocation network id -1 needs to be a positive integer."
+end
+
+@testitem "Incomplete subnetwork" begin
+    using MetaGraphsNext
+    using Graphs
+    using Logging
+    using Ribasim
+
+    graph = MetaGraph(
+        DiGraph();
+        label_type = Ribasim.NodeID,
+        vertex_data_type = Ribasim.NodeMetadata,
+        edge_data_type = Symbol,
+        graph_data = Tuple,
+    )
+
+    node_ids = Dict{Int, Set{Ribasim.NodeID}}()
+    node_ids[1] = Set{Ribasim.NodeID}()
+    push!(node_ids[1], Ribasim.NodeID(1))
+    push!(node_ids[1], Ribasim.NodeID(2))
+    push!(node_ids[1], Ribasim.NodeID(3))
+    node_ids[2] = Set{Ribasim.NodeID}()
+    push!(node_ids[2], Ribasim.NodeID(4))
+    push!(node_ids[2], Ribasim.NodeID(5))
+    push!(node_ids[2], Ribasim.NodeID(6))
+
+    graph[Ribasim.NodeID(1)] = Ribasim.NodeMetadata(Symbol(:delft), 1)
+    graph[Ribasim.NodeID(2)] = Ribasim.NodeMetadata(Symbol(:denhaag), 1)
+    graph[Ribasim.NodeID(3)] = Ribasim.NodeMetadata(Symbol(:rdam), 1)
+    graph[Ribasim.NodeID(4)] = Ribasim.NodeMetadata(Symbol(:adam), 2)
+    graph[Ribasim.NodeID(5)] = Ribasim.NodeMetadata(Symbol(:utrecht), 2)
+    graph[Ribasim.NodeID(6)] = Ribasim.NodeMetadata(Symbol(:leiden), 2)
+
+    graph[Ribasim.NodeID(1), Ribasim.NodeID(2)] = :yes
+    graph[Ribasim.NodeID(1), Ribasim.NodeID(3)] = :yes
+    graph[4, 5] = :yes
+
+    logger = TestLogger()
+
+    with_logger(logger) do
+        errors = Ribasim.incomplete_subnetwork(graph, node_ids)
+        @test errors == true
+    end
+
+    @test length(logger.logs) == 1
+    @test logger.logs[1].level == Error
+    @test logger.logs[1].message == "All nodes in subnetwork 2 should be connected"
+end
diff --git a/core/test/validation_test.jl b/core/test/validation_test.jl
index 97b782b6d..62d8cfeb7 100644
--- a/core/test/validation_test.jl
+++ b/core/test/validation_test.jl
@@ -401,3 +401,27 @@ end
     @test logger.logs[2].message ==
           "Basin / subgrid_level subgrid_id 1 has repeated element levels, this cannot be interpolated."
 end
+
+@testitem "negative demand" begin
+    using Logging
+    using DataInterpolations: LinearInterpolation
+    logger = TestLogger()
+
+    with_logger(logger) do
+        @test_throws "Invalid demand" Ribasim.User(
+            [Ribasim.NodeID(1)],
+            [true],
+            [[LinearInterpolation([-5.0, -5.0], [-1.8, 1.8])]],
+            [0.0, -0.0],
+            [0.9],
+            [0.9],
+            [1],
+            [],
+        )
+    end
+
+    @test length(logger.logs) == 1
+    @test logger.logs[1].level == Error
+    @test logger.logs[1].message ==
+          "Demand of user node #1 with priority 1 should be non-negative"
+end